source: draft-ietf-httpbis/latest/p1-messaging.xml @ 1159

Last change on this file since 1159 was 1159, checked in by julian.reschke@…, 11 years ago

note change [1157], see #159

  • Property svn:eol-style set to native
File size: 249.6 KB
1<?xml version="1.0" encoding="utf-8"?>
2<?xml-stylesheet type='text/xsl' href='../myxml2rfc.xslt'?>
3<!DOCTYPE rfc [
4  <!ENTITY MAY "<bcp14 xmlns=''>MAY</bcp14>">
5  <!ENTITY MUST "<bcp14 xmlns=''>MUST</bcp14>">
6  <!ENTITY MUST-NOT "<bcp14 xmlns=''>MUST NOT</bcp14>">
7  <!ENTITY OPTIONAL "<bcp14 xmlns=''>OPTIONAL</bcp14>">
8  <!ENTITY RECOMMENDED "<bcp14 xmlns=''>RECOMMENDED</bcp14>">
9  <!ENTITY REQUIRED "<bcp14 xmlns=''>REQUIRED</bcp14>">
10  <!ENTITY SHALL "<bcp14 xmlns=''>SHALL</bcp14>">
11  <!ENTITY SHALL-NOT "<bcp14 xmlns=''>SHALL NOT</bcp14>">
12  <!ENTITY SHOULD "<bcp14 xmlns=''>SHOULD</bcp14>">
13  <!ENTITY SHOULD-NOT "<bcp14 xmlns=''>SHOULD NOT</bcp14>">
14  <!ENTITY ID-VERSION "latest">
15  <!ENTITY ID-MONTH "March">
16  <!ENTITY ID-YEAR "2011">
17  <!ENTITY mdash "&#8212;">
18  <!ENTITY caching-overview       "<xref target='Part6' x:rel='#caching.overview' xmlns:x=''/>">
19  <!ENTITY cache-incomplete       "<xref target='Part6' x:rel='#errors.or.incomplete.response.cache.behavior' xmlns:x=''/>">
20  <!ENTITY payload                "<xref target='Part3' xmlns:x=''/>">
21  <!ENTITY media-types            "<xref target='Part3' x:rel='#media.types' xmlns:x=''/>">
22  <!ENTITY content-codings        "<xref target='Part3' x:rel='#content.codings' xmlns:x=''/>">
23  <!ENTITY CONNECT                "<xref target='Part2' x:rel='#CONNECT' xmlns:x=''/>">
24  <!ENTITY content.negotiation    "<xref target='Part3' x:rel='#content.negotiation' xmlns:x=''/>">
25  <!ENTITY diff-mime              "<xref target='Part3' x:rel='#differences.between.http.and.mime' xmlns:x=''/>">
26  <!ENTITY representation         "<xref target='Part3' x:rel='#representation' xmlns:x=''/>">
27  <!ENTITY header-cache-control   "<xref target='Part6' x:rel='#header.cache-control' xmlns:x=''/>">
28  <!ENTITY header-expect          "<xref target='Part2' x:rel='#header.expect' xmlns:x=''/>">
29  <!ENTITY header-mime-version    "<xref target='Part3' x:rel='#mime-version' xmlns:x=''/>">
30  <!ENTITY header-pragma          "<xref target='Part6' x:rel='#header.pragma' xmlns:x=''/>">
31  <!ENTITY header-warning         "<xref target='Part6' x:rel='#header.warning' xmlns:x=''/>">
32  <!ENTITY idempotent-methods     "<xref target='Part2' x:rel='#idempotent.methods' xmlns:x=''/>">
33  <!ENTITY request-header-fields  "<xref target='Part2' x:rel='#request.header.fields' xmlns:x=''/>">
34  <!ENTITY response-header-fields "<xref target='Part2' x:rel='#response.header.fields' xmlns:x=''/>">
35  <!ENTITY status-codes           "<xref target='Part2' x:rel='' xmlns:x=''/>">
36  <!ENTITY status-100             "<xref target='Part2' x:rel='#status.100' xmlns:x=''/>">
37  <!ENTITY status-1xx             "<xref target='Part2' x:rel='#status.1xx' xmlns:x=''/>">
38  <!ENTITY status-3xx             "<xref target='Part2' x:rel='#status.3xx' xmlns:x=''/>">
39  <!ENTITY status-414             "<xref target='Part2' x:rel='#status.414' xmlns:x=''/>">
41<?rfc toc="yes" ?>
42<?rfc symrefs="yes" ?>
43<?rfc sortrefs="yes" ?>
44<?rfc compact="yes"?>
45<?rfc subcompact="no" ?>
46<?rfc linkmailto="no" ?>
47<?rfc editing="no" ?>
48<?rfc comments="yes"?>
49<?rfc inline="yes"?>
50<?rfc rfcedstyle="yes"?>
51<?rfc-ext allow-markup-in-artwork="yes" ?>
52<?rfc-ext include-references-in-index="yes" ?>
53<rfc obsoletes="2145,2616" updates="2817" category="std" x:maturity-level="draft"
54     ipr="pre5378Trust200902" docName="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"
55     xmlns:x=''>
58  <title abbrev="HTTP/1.1, Part 1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
60  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
61    <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
62    <address>
63      <postal>
64        <street>345 Park Ave</street>
65        <city>San Jose</city>
66        <region>CA</region>
67        <code>95110</code>
68        <country>USA</country>
69      </postal>
70      <email></email>
71      <uri></uri>
72    </address>
73  </author>
75  <author initials="J." surname="Gettys" fullname="Jim Gettys">
76    <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
77    <address>
78      <postal>
79        <street>21 Oak Knoll Road</street>
80        <city>Carlisle</city>
81        <region>MA</region>
82        <code>01741</code>
83        <country>USA</country>
84      </postal>
85      <email></email>
86      <uri></uri>
87    </address>
88  </author>
90  <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
91    <organization abbrev="HP">Hewlett-Packard Company</organization>
92    <address>
93      <postal>
94        <street>HP Labs, Large Scale Systems Group</street>
95        <street>1501 Page Mill Road, MS 1177</street>
96        <city>Palo Alto</city>
97        <region>CA</region>
98        <code>94304</code>
99        <country>USA</country>
100      </postal>
101      <email></email>
102    </address>
103  </author>
105  <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
106    <organization abbrev="Microsoft">Microsoft Corporation</organization>
107    <address>
108      <postal>
109        <street>1 Microsoft Way</street>
110        <city>Redmond</city>
111        <region>WA</region>
112        <code>98052</code>
113        <country>USA</country>
114      </postal>
115      <email></email>
116    </address>
117  </author>
119  <author initials="L." surname="Masinter" fullname="Larry Masinter">
120    <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
121    <address>
122      <postal>
123        <street>345 Park Ave</street>
124        <city>San Jose</city>
125        <region>CA</region>
126        <code>95110</code>
127        <country>USA</country>
128      </postal>
129      <email></email>
130      <uri></uri>
131    </address>
132  </author>
134  <author initials="P." surname="Leach" fullname="Paul J. Leach">
135    <organization abbrev="Microsoft">Microsoft Corporation</organization>
136    <address>
137      <postal>
138        <street>1 Microsoft Way</street>
139        <city>Redmond</city>
140        <region>WA</region>
141        <code>98052</code>
142      </postal>
143      <email></email>
144    </address>
145  </author>
147  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
148    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
149    <address>
150      <postal>
151        <street>MIT Computer Science and Artificial Intelligence Laboratory</street>
152        <street>The Stata Center, Building 32</street>
153        <street>32 Vassar Street</street>
154        <city>Cambridge</city>
155        <region>MA</region>
156        <code>02139</code>
157        <country>USA</country>
158      </postal>
159      <email></email>
160      <uri></uri>
161    </address>
162  </author>
164  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
165    <organization abbrev="W3C">World Wide Web Consortium</organization>
166    <address>
167      <postal>
168        <street>W3C / ERCIM</street>
169        <street>2004, rte des Lucioles</street>
170        <city>Sophia-Antipolis</city>
171        <region>AM</region>
172        <code>06902</code>
173        <country>France</country>
174      </postal>
175      <email></email>
176      <uri></uri>
177    </address>
178  </author>
180  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
181    <organization abbrev="greenbytes">greenbytes GmbH</organization>
182    <address>
183      <postal>
184        <street>Hafenweg 16</street>
185        <city>Muenster</city><region>NW</region><code>48155</code>
186        <country>Germany</country>
187      </postal>
188      <phone>+49 251 2807760</phone>
189      <facsimile>+49 251 2807761</facsimile>
190      <email></email>
191      <uri></uri>
192    </address>
193  </author>
195  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
196  <workgroup>HTTPbis Working Group</workgroup>
200   The Hypertext Transfer Protocol (HTTP) is an application-level
201   protocol for distributed, collaborative, hypertext information
202   systems. HTTP has been in use by the World Wide Web global information
203   initiative since 1990. This document is Part 1 of the seven-part specification
204   that defines the protocol referred to as "HTTP/1.1" and, taken together,
205   obsoletes RFC 2616.  Part 1 provides an overview of HTTP and
206   its associated terminology, defines the "http" and "https" Uniform
207   Resource Identifier (URI) schemes, defines the generic message syntax
208   and parsing requirements for HTTP message frames, and describes
209   general security concerns for implementations.
213<note title="Editorial Note (To be removed by RFC Editor)">
214  <t>
215    Discussion of this draft should take place on the HTTPBIS working group
216    mailing list ( The current issues list is
217    at <eref target=""/>
218    and related documents (including fancy diffs) can be found at
219    <eref target=""/>.
220  </t>
221  <t>
222    The changes in this draft are summarized in <xref target="changes.since.12"/>.
223  </t>
227<section title="Introduction" anchor="introduction">
229   The Hypertext Transfer Protocol (HTTP) is an application-level
230   request/response protocol that uses extensible semantics and MIME-like
231   message payloads for flexible interaction with network-based hypertext
232   information systems. HTTP relies upon the Uniform Resource Identifier (URI)
233   standard <xref target="RFC3986"/> to indicate request targets and
234   relationships between resources.
235   Messages are passed in a format similar to that used by Internet mail
236   <xref target="RFC5322"/> and the Multipurpose Internet Mail Extensions
237   (MIME) <xref target="RFC2045"/> (see &diff-mime; for the differences
238   between HTTP and MIME messages).
241   HTTP is a generic interface protocol for information systems. It is
242   designed to hide the details of how a service is implemented by presenting
243   a uniform interface to clients that is independent of the types of
244   resources provided. Likewise, servers do not need to be aware of each
245   client's purpose: an HTTP request can be considered in isolation rather
246   than being associated with a specific type of client or a predetermined
247   sequence of application steps. The result is a protocol that can be used
248   effectively in many different contexts and for which implementations can
249   evolve independently over time.
252   HTTP is also designed for use as an intermediation protocol for translating
253   communication to and from non-HTTP information systems.
254   HTTP proxies and gateways can provide access to alternative information
255   services by translating their diverse protocols into a hypertext
256   format that can be viewed and manipulated by clients in the same way
257   as HTTP services.
260   One consequence of HTTP flexibility is that the protocol cannot be
261   defined in terms of what occurs behind the interface. Instead, we
262   are limited to defining the syntax of communication, the intent
263   of received communication, and the expected behavior of recipients.
264   If the communication is considered in isolation, then successful
265   actions ought to be reflected in corresponding changes to the
266   observable interface provided by servers. However, since multiple
267   clients might act in parallel and perhaps at cross-purposes, we
268   cannot require that such changes be observable beyond the scope
269   of a single response.
272   This document is Part 1 of the seven-part specification of HTTP,
273   defining the protocol referred to as "HTTP/1.1", obsoleting
274   <xref target="RFC2616"/> and <xref target="RFC2145"/>.
275   Part 1 describes the architectural elements that are used or
276   referred to in HTTP, defines the "http" and "https" URI schemes,
277   describes overall network operation and connection management,
278   and defines HTTP message framing and forwarding requirements.
279   Our goal is to define all of the mechanisms necessary for HTTP message
280   handling that are independent of message semantics, thereby defining the
281   complete set of requirements for message parsers and
282   message-forwarding intermediaries.
285<section title="Requirements" anchor="intro.requirements">
287   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
288   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
289   document are to be interpreted as described in <xref target="RFC2119"/>.
292   An implementation is not compliant if it fails to satisfy one or more
293   of the "MUST" or "REQUIRED" level requirements for the protocols it
294   implements. An implementation that satisfies all the "MUST" or "REQUIRED"
295   level and all the "SHOULD" level requirements for its protocols is said
296   to be "unconditionally compliant"; one that satisfies all the "MUST"
297   level requirements but not all the "SHOULD" level requirements for its
298   protocols is said to be "conditionally compliant".
302<section title="Syntax Notation" anchor="notation">
303<iref primary="true" item="Grammar" subitem="ALPHA"/>
304<iref primary="true" item="Grammar" subitem="CR"/>
305<iref primary="true" item="Grammar" subitem="CRLF"/>
306<iref primary="true" item="Grammar" subitem="CTL"/>
307<iref primary="true" item="Grammar" subitem="DIGIT"/>
308<iref primary="true" item="Grammar" subitem="DQUOTE"/>
309<iref primary="true" item="Grammar" subitem="HEXDIG"/>
310<iref primary="true" item="Grammar" subitem="LF"/>
311<iref primary="true" item="Grammar" subitem="OCTET"/>
312<iref primary="true" item="Grammar" subitem="SP"/>
313<iref primary="true" item="Grammar" subitem="VCHAR"/>
314<iref primary="true" item="Grammar" subitem="WSP"/>
316   This specification uses the Augmented Backus-Naur Form (ABNF) notation
317   of <xref target="RFC5234"/>.
319<t anchor="core.rules">
320  <x:anchor-alias value="ALPHA"/>
321  <x:anchor-alias value="CTL"/>
322  <x:anchor-alias value="CR"/>
323  <x:anchor-alias value="CRLF"/>
324  <x:anchor-alias value="DIGIT"/>
325  <x:anchor-alias value="DQUOTE"/>
326  <x:anchor-alias value="HEXDIG"/>
327  <x:anchor-alias value="LF"/>
328  <x:anchor-alias value="OCTET"/>
329  <x:anchor-alias value="SP"/>
330  <x:anchor-alias value="VCHAR"/>
331  <x:anchor-alias value="WSP"/>
332   The following core rules are included by
333   reference, as defined in <xref target="RFC5234" x:fmt="," x:sec="B.1"/>:
334   ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
335   DIGIT (decimal 0-9), DQUOTE (double quote),
336   HEXDIG (hexadecimal 0-9/A-F/a-f), LF (line feed),
337   OCTET (any 8-bit sequence of data), SP (space),
338   VCHAR (any visible <xref target="USASCII"/> character),
339   and WSP (whitespace).
342   As a syntactic convention, ABNF rule names prefixed with "obs-" denote
343   "obsolete" grammar rules that appear for historical reasons.
346<section title="ABNF Extension: #rule" anchor="notation.abnf">
348  The #rule extension to the ABNF rules of <xref target="RFC5234"/> is used to
349  improve readability.
352  A construct "#" is defined, similar to "*", for defining comma-delimited
353  lists of elements. The full form is "&lt;n&gt;#&lt;m&gt;element" indicating
354  at least &lt;n&gt; and at most &lt;m&gt; elements, each separated by a single
355  comma (",") and optional whitespace (OWS,
356  <xref target="basic.rules"/>).   
359  Thus,
360</preamble><artwork type="example">
361  1#element =&gt; element *( OWS "," OWS element )
364  and:
365</preamble><artwork type="example">
366  #element =&gt; [ 1#element ]
369  and for n &gt;= 1 and m &gt; 1:
370</preamble><artwork type="example">
371  &lt;n&gt;#&lt;m&gt;element =&gt; element &lt;n-1&gt;*&lt;m-1&gt;( OWS "," OWS element )
374  For compatibility with legacy list rules, recipients &SHOULD; accept empty
375  list elements. In other words, consumers would follow the list productions:
377<figure><artwork type="example">
378  #element =&gt; [ ( "," / element ) *( OWS "," [ OWS element ] ) ]
380  1#element =&gt; *( "," OWS ) element *( OWS "," [ OWS element ] )
383  Note that empty elements do not contribute to the count of elements present,
384  though.
387  For example, given these ABNF productions:
389<figure><artwork type="example">
390  example-list      = 1#example-list-elmt
391  example-list-elmt = token ; see <xref target="basic.rules"/>
394  Then these are valid values for example-list (not including the double
395  quotes, which are present for delimitation only):
397<figure><artwork type="example">
398  "foo,bar"
399  " foo ,bar,"
400  "  foo , ,bar,charlie   "
401  "foo ,bar,   charlie "
404  But these values would be invalid, as at least one non-empty element is
405  required:
407<figure><artwork type="example">
408  ""
409  ","
410  ",   ,"
413  <xref target="collected.abnf"/> shows the collected ABNF, with the list rules
414  expanded as explained above.
418<section title="Basic Rules" anchor="basic.rules">
419<t anchor="rule.CRLF">
420  <x:anchor-alias value="CRLF"/>
421   HTTP/1.1 defines the sequence CR LF as the end-of-line marker for all
422   protocol elements other than the message-body
423   (see <xref target="tolerant.applications"/> for tolerant applications).
425<t anchor="rule.LWS">
426   This specification uses three rules to denote the use of linear
427   whitespace: OWS (optional whitespace), RWS (required whitespace), and
428   BWS ("bad" whitespace).
431   The OWS rule is used where zero or more linear whitespace characters might
432   appear. OWS &SHOULD; either not be produced or be produced as a single SP
433   character. Multiple OWS characters that occur within field-content &SHOULD;
434   be replaced with a single SP before interpreting the field value or
435   forwarding the message downstream.
438   RWS is used when at least one linear whitespace character is required to
439   separate field tokens. RWS &SHOULD; be produced as a single SP character.
440   Multiple RWS characters that occur within field-content &SHOULD; be
441   replaced with a single SP before interpreting the field value or
442   forwarding the message downstream.
445   BWS is used where the grammar allows optional whitespace for historical
446   reasons but senders &SHOULD-NOT; produce it in messages. HTTP/1.1
447   recipients &MUST; accept such bad optional whitespace and remove it before
448   interpreting the field value or forwarding the message downstream.
450<t anchor="rule.whitespace">
451  <x:anchor-alias value="BWS"/>
452  <x:anchor-alias value="OWS"/>
453  <x:anchor-alias value="RWS"/>
454  <x:anchor-alias value="obs-fold"/>
456<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="OWS"/><iref primary="true" item="Grammar" subitem="RWS"/><iref primary="true" item="Grammar" subitem="BWS"/>
457  <x:ref>OWS</x:ref>            = *( [ obs-fold ] <x:ref>WSP</x:ref> )
458                 ; "optional" whitespace
459  <x:ref>RWS</x:ref>            = 1*( [ obs-fold ] <x:ref>WSP</x:ref> )
460                 ; "required" whitespace
461  <x:ref>BWS</x:ref>            = <x:ref>OWS</x:ref>
462                 ; "bad" whitespace
463  <x:ref>obs-fold</x:ref>       = <x:ref>CRLF</x:ref>
464                 ; see <xref target="header.fields"/>
466<t anchor="rule.token.separators">
467  <x:anchor-alias value="tchar"/>
468  <x:anchor-alias value="token"/>
469  <x:anchor-alias value="special"/>
470  <x:anchor-alias value="word"/>
471   Many HTTP/1.1 header field values consist of words (token or quoted-string)
472   separated by whitespace or special characters. These special characters
473   &MUST; be in a quoted string to be used within a parameter value (as defined
474   in <xref target="transfer.codings"/>).
476<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="word"/><iref primary="true" item="Grammar" subitem="token"/><iref primary="true" item="Grammar" subitem="tchar"/><iref primary="true" item="Grammar" subitem="special"/>
477  <x:ref>word</x:ref>           = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
479  <x:ref>token</x:ref>          = 1*<x:ref>tchar</x:ref>
481  IMPORTANT: when editing "tchar" make sure that "special" is updated accordingly!!!
482 -->
483  <x:ref>tchar</x:ref>          = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*"
484                 / "+" / "-" / "." / "^" / "_" / "`" / "|" / "~"
485                 / <x:ref>DIGIT</x:ref> / <x:ref>ALPHA</x:ref>
486                 ; any <x:ref>VCHAR</x:ref>, except <x:ref>special</x:ref>
488  <x:ref>special</x:ref>        = "(" / ")" / "&lt;" / ">" / "@" / ","
489                 / ";" / ":" / "\" / DQUOTE / "/" / "["
490                 / "]" / "?" / "=" / "{" / "}"
492<t anchor="rule.quoted-string">
493  <x:anchor-alias value="quoted-string"/>
494  <x:anchor-alias value="qdtext"/>
495  <x:anchor-alias value="obs-text"/>
496   A string of text is parsed as a single word if it is quoted using
497   double-quote marks.
499<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-string"/><iref primary="true" item="Grammar" subitem="qdtext"/><iref primary="true" item="Grammar" subitem="obs-text"/>
500  <x:ref>quoted-string</x:ref>  = <x:ref>DQUOTE</x:ref> *( <x:ref>qdtext</x:ref> / <x:ref>quoted-pair</x:ref> ) <x:ref>DQUOTE</x:ref>
501  <x:ref>qdtext</x:ref>         = <x:ref>OWS</x:ref> / %x21 / %x23-5B / %x5D-7E / <x:ref>obs-text</x:ref>
502                 ; <x:ref>OWS</x:ref> / &lt;<x:ref>VCHAR</x:ref> except <x:ref>DQUOTE</x:ref> and "\"&gt; / <x:ref>obs-text</x:ref>
503  <x:ref>obs-text</x:ref>       = %x80-FF
505<t anchor="rule.quoted-pair">
506  <x:anchor-alias value="quoted-pair"/>
507   The backslash character ("\") can be used as a single-character
508   quoting mechanism within quoted-string constructs:
510<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-pair"/>
511  <x:ref>quoted-pair</x:ref>    = "\" ( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
514   Producers &SHOULD-NOT; escape characters that do not require escaping
515   (i.e., other than DQUOTE and the backslash character).
519<section title="ABNF Rules defined in other Parts of the Specification" anchor="abnf.dependencies">
520  <x:anchor-alias value="request-header"/>
521  <x:anchor-alias value="response-header"/>
522  <x:anchor-alias value="Cache-Control"/>
523  <x:anchor-alias value="Pragma"/>
524  <x:anchor-alias value="Warning"/>
525  <x:anchor-alias value="MIME-Version"/>
527  The ABNF rules below are defined in other parts:
529<figure><!-- Part2--><artwork type="abnf2616">
530  <x:ref>request-header</x:ref>  = &lt;request-header, defined in &request-header-fields;&gt;
531  <x:ref>response-header</x:ref> = &lt;response-header, defined in &response-header-fields;&gt;
533<figure><!-- Part3--><artwork type="abnf2616">
534  <x:ref>MIME-Version</x:ref>    = &lt;MIME-Version, defined in &header-mime-version;&gt;
536<figure><!-- Part6--><artwork type="abnf2616">
537  <x:ref>Cache-Control</x:ref>   = &lt;Cache-Control, defined in &header-pragma;&gt;
538  <x:ref>Pragma</x:ref>          = &lt;Pragma, defined in &header-pragma;&gt;
539  <x:ref>Warning</x:ref>         = &lt;Warning, defined in &header-warning;&gt;
546<section title="HTTP-related architecture" anchor="architecture">
548   HTTP was created for the World Wide Web architecture
549   and has evolved over time to support the scalability needs of a worldwide
550   hypertext system. Much of that architecture is reflected in the terminology
551   and syntax productions used to define HTTP.
554<section title="Client/Server Messaging" anchor="operation">
555<iref primary="true" item="client"/>
556<iref primary="true" item="server"/>
557<iref primary="true" item="connection"/>
559   HTTP is a stateless request/response protocol that operates by exchanging
560   messages across a reliable transport or session-layer connection. An HTTP
561   "client" is a program that establishes a connection to a server for the
562   purpose of sending one or more HTTP requests.  An HTTP "server" is a
563   program that accepts connections in order to service HTTP requests by
564   sending HTTP responses.
566<iref primary="true" item="user agent"/>
567<iref primary="true" item="origin server"/>
568<iref primary="true" item="browser"/>
569<iref primary="true" item="spider"/>
571   Note that the terms client and server refer only to the roles that
572   these programs perform for a particular connection.  The same program
573   might act as a client on some connections and a server on others.  We use
574   the term "user agent" to refer to the program that initiates a request,
575   such as a WWW browser, editor, or spider (web-traversing robot), and
576   the term "origin server" to refer to the program that can originate
577   authoritative responses to a request.  For general requirements, we use
578   the term "sender" to refer to whichever component sent a given message
579   and the term "recipient" to refer to any component that receives the
580   message.
583   Most HTTP communication consists of a retrieval request (GET) for
584   a representation of some resource identified by a URI.  In the
585   simplest case, this might be accomplished via a single bidirectional
586   connection (===) between the user agent (UA) and the origin server (O).
588<figure><artwork type="drawing">
589         request   &gt;
590    UA ======================================= O
591                                &lt;   response
593<iref primary="true" item="message"/>
594<iref primary="true" item="request"/>
595<iref primary="true" item="response"/>
597   A client sends an HTTP request to the server in the form of a request
598   message (<xref target="request"/>), beginning with a method, URI, and
599   protocol version, followed by MIME-like header fields containing
600   request modifiers, client information, and payload metadata, an empty
601   line to indicate the end of the header section, and finally the payload
602   body (if any).
605   A server responds to the client's request by sending an HTTP response
606   message (<xref target="response"/>), beginning with a status line that
607   includes the protocol version, a success or error code, and textual
608   reason phrase, followed by MIME-like header fields containing server
609   information, resource metadata, and payload metadata, an empty line to
610   indicate the end of the header section, and finally the payload body (if any).
613   The following example illustrates a typical message exchange for a
614   GET request on the URI "":
617client request:
618</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
619GET /hello.txt HTTP/1.1
620User-Agent: curl/7.16.3 libcurl/7.16.3 OpenSSL/0.9.7l zlib/1.2.3
622Accept: */*
626server response:
627</preamble><artwork type="message/http; msgtype=&#34;response&#34;" x:indent-with="  ">
628HTTP/1.1 200 OK
629Date: Mon, 27 Jul 2009 12:28:53 GMT
630Server: Apache
631Last-Modified: Wed, 22 Jul 2009 19:15:56 GMT
632ETag: "34aa387-d-1568eb00"
633Accept-Ranges: bytes
634Content-Length: <x:length-of target="exbody"/>
635Vary: Accept-Encoding
636Content-Type: text/plain
638<x:span anchor="exbody">Hello World!
642<section title="Connections and Transport Independence" anchor="transport-independence">
644   HTTP messaging is independent of the underlying transport or
645   session-layer connection protocol(s).  HTTP only presumes a reliable
646   transport with in-order delivery of requests and the corresponding
647   in-order delivery of responses.  The mapping of HTTP request and
648   response structures onto the data units of the underlying transport
649   protocol is outside the scope of this specification.
652   The specific connection protocols to be used for an interaction
653   are determined by client configuration and the identifier (if any)
654   provided for the request target.  For example, the "http" URI scheme
655   (<xref target="http.uri"/>) indicates a default connection of TCP
656   over IP, with a default TCP port of 80, but the client might be
657   configured to use a proxy via some other connection port or protocol
658   instead of using the defaults.
661   A connection might be used for multiple HTTP request/response exchanges,
662   as defined in <xref target="persistent.connections"/>.
666<section title="Intermediaries" anchor="intermediaries">
667<iref primary="true" item="intermediary"/>
669   HTTP enables the use of intermediaries to satisfy requests through
670   a chain of connections.  There are three common forms of HTTP
671   intermediary: proxy, gateway, and tunnel.  In some cases,
672   a single intermediary might act as an origin server, proxy, gateway,
673   or tunnel, switching behavior based on the nature of each request.
675<figure><artwork type="drawing">
676         &gt;             &gt;             &gt;             &gt;
677    UA =========== A =========== B =========== C =========== O
678               &lt;             &lt;             &lt;             &lt;
681   The figure above shows three intermediaries (A, B, and C) between the
682   user agent and origin server. A request or response message that
683   travels the whole chain will pass through four separate connections.
684   Some HTTP communication options
685   might apply only to the connection with the nearest, non-tunnel
686   neighbor, only to the end-points of the chain, or to all connections
687   along the chain. Although the diagram is linear, each participant might
688   be engaged in multiple, simultaneous communications. For example, B
689   might be receiving requests from many clients other than A, and/or
690   forwarding requests to servers other than C, at the same time that it
691   is handling A's request.
694<iref primary="true" item="upstream"/><iref primary="true" item="downstream"/>
695<iref primary="true" item="inbound"/><iref primary="true" item="outbound"/>
696   We use the terms "upstream" and "downstream" to describe various
697   requirements in relation to the directional flow of a message:
698   all messages flow from upstream to downstream.
699   Likewise, we use the terms "inbound" and "outbound" to refer to
700   directions in relation to the request path: "inbound" means toward
701   the origin server and "outbound" means toward the user agent.
703<t><iref primary="true" item="proxy"/>
704   A "proxy" is a message forwarding agent that is selected by the
705   client, usually via local configuration rules, to receive requests
706   for some type(s) of absolute URI and attempt to satisfy those
707   requests via translation through the HTTP interface.  Some translations
708   are minimal, such as for proxy requests for "http" URIs, whereas
709   other requests might require translation to and from entirely different
710   application-layer protocols. Proxies are often used to group an
711   organization's HTTP requests through a common intermediary for the
712   sake of security, annotation services, or shared caching.
715<iref primary="true" item="transforming proxy"/>
716<iref primary="true" item="non-transforming proxy"/>
717   An HTTP-to-HTTP proxy is called a "transforming proxy" if it is designed
718   or configured to modify request or response messages in a semantically
719   meaningful way (i.e., modifications, beyond those required by normal
720   HTTP processing, that change the message in a way that would be
721   significant to the original sender or potentially significant to
722   downstream recipients).  For example, a transforming proxy might be
723   acting as a shared annotation server (modifying responses to include
724   references to a local annotation database), a malware filter, a
725   format transcoder, or an intranet-to-Internet privacy filter.  Such
726   transformations are presumed to be desired by the client (or client
727   organization) that selected the proxy and are beyond the scope of
728   this specification.  However, when a proxy is not intended to transform
729   a given message, we use the term "non-transforming proxy" to target
730   requirements that preserve HTTP message semantics.
732<t><iref primary="true" item="gateway"/><iref primary="true" item="reverse proxy"/>
733   A "gateway" (a.k.a., "reverse proxy") is a receiving agent that acts
734   as a layer above some other server(s) and translates the received
735   requests to the underlying server's protocol.  Gateways are often
736   used for load balancing or partitioning HTTP services across
737   multiple machines.
738   Unlike a proxy, a gateway receives requests as if it were the
739   origin server for the target resource; the requesting client
740   will not be aware that it is communicating with a gateway.
741   A gateway communicates with the client as if the gateway is the
742   origin server and thus is subject to all of the requirements on
743   origin servers for that connection.  A gateway communicates
744   with inbound servers using any protocol it desires, including
745   private extensions to HTTP that are outside the scope of this
746   specification.
748<t><iref primary="true" item="tunnel"/>
749   A "tunnel" acts as a blind relay between two connections
750   without changing the messages. Once active, a tunnel is not
751   considered a party to the HTTP communication, though the tunnel might
752   have been initiated by an HTTP request. A tunnel ceases to exist when
753   both ends of the relayed connection are closed. Tunnels are used to
754   extend a virtual connection through an intermediary, such as when
755   transport-layer security is used to establish private communication
756   through a shared firewall proxy.
758<t><iref primary="true" item="interception proxy"/><iref primary="true" item="transparent proxy"/>
759   In addition, there may exist network intermediaries that are not
760   considered part of the HTTP communication but nevertheless act as
761   filters or redirecting agents (usually violating HTTP semantics,
762   causing security problems, and otherwise making a mess of things).
763   Such a network intermediary, referred to as an "interception proxy"
764   <xref target="RFC3040"/> or "transparent proxy" <xref target="RFC1919"/>,
765   differs from an HTTP proxy because it has not been selected by the client.
766   Instead, the network intermediary redirects outgoing TCP port 80 packets
767   (and occasionally other common port traffic) to an internal HTTP server.
768   Interception proxies are commonly found on public network access points
769   as a means of enforcing account subscription prior to allowing use of
770   non-local Internet services.  They are indistinguishable from a
771   man-in-the-middle attack.
775<section title="Caches" anchor="caches">
776<iref primary="true" item="cache"/>
778   A "cache" is a local store of previous response messages and the
779   subsystem that controls its message storage, retrieval, and deletion.
780   A cache stores cacheable responses in order to reduce the response
781   time and network bandwidth consumption on future, equivalent
782   requests. Any client or server &MAY; employ a cache, though a cache
783   cannot be used by a server while it is acting as a tunnel.
786   The effect of a cache is that the request/response chain is shortened
787   if one of the participants along the chain has a cached response
788   applicable to that request. The following illustrates the resulting
789   chain if B has a cached copy of an earlier response from O (via C)
790   for a request which has not been cached by UA or A.
792<figure><artwork type="drawing">
793            &gt;             &gt;
794       UA =========== A =========== B - - - - - - C - - - - - - O
795                  &lt;             &lt;
797<t><iref primary="true" item="cacheable"/>
798   A response is "cacheable" if a cache is allowed to store a copy of
799   the response message for use in answering subsequent requests.
800   Even when a response is cacheable, there might be additional
801   constraints placed by the client or by the origin server on when
802   that cached response can be used for a particular request. HTTP
803   requirements for cache behavior and cacheable responses are
804   defined in &caching-overview;. 
807   There are a wide variety of architectures and configurations
808   of caches and proxies deployed across the World Wide Web and
809   inside large organizations. These systems include national hierarchies
810   of proxy caches to save transoceanic bandwidth, systems that
811   broadcast or multicast cache entries, organizations that distribute
812   subsets of cached data via optical media, and so on.
816<section title="Protocol Versioning" anchor="http.version">
817  <x:anchor-alias value="HTTP-Version"/>
818  <x:anchor-alias value="HTTP-Prot-Name"/>
820   HTTP uses a "&lt;major&gt;.&lt;minor&gt;" numbering scheme to indicate
821   versions of the protocol. This specification defines version "1.1".
822   The protocol version as a whole indicates the sender's compliance
823   with the set of requirements laid out in that version's corresponding
824   specification of HTTP.
827   The version of an HTTP message is indicated by an HTTP-Version field
828   in the first line of the message. HTTP-Version is case-sensitive.
830<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-Version"/><iref primary="true" item="Grammar" subitem="HTTP-Prot-Name"/>
831  <x:ref>HTTP-Version</x:ref>   = <x:ref>HTTP-Prot-Name</x:ref> "/" 1*<x:ref>DIGIT</x:ref> "." 1*<x:ref>DIGIT</x:ref>
832  <x:ref>HTTP-Prot-Name</x:ref> = <x:abnf-char-sequence>"HTTP"</x:abnf-char-sequence> ; "HTTP", case-sensitive
835   The HTTP version number consists of two non-negative decimal integers
836   separated by the "." (period or decimal point) character.  The first
837   number ("major version") indicates the HTTP messaging syntax, whereas
838   the second number ("minor version") indicates the highest minor
839   version to which the sender is at least conditionally compliant and
840   able to understand for future communication.  The minor version
841   advertises the sender's communication capabilities even when the
842   sender is only using a backwards-compatible subset of the protocol,
843   thereby letting the recipient know that more advanced features can
844   be used in response (by servers) or in future requests (by clients).
847   When comparing HTTP versions, the numbers &MUST; be compared
848   numerically rather than lexically.  For example, HTTP/2.4 is a lower
849   version than HTTP/2.13, which in turn is lower than HTTP/12.3.
850   Leading zeros &MUST; be ignored by recipients and &MUST-NOT; be sent.
853   When an HTTP/1.1 message is sent to an HTTP/1.0 recipient
854   (or a recipient whose version is unknown), the HTTP/1.1 message is
855   constructed such that it will be interpreted as a valid HTTP/1.0
856   message even if all of the provided header fields not defined in
857   the HTTP/1.0 specification <xref target="RFC1945"/> are ignored.
858   This specification excludes incompatible message constructions by
859   imposing recipient-version requirements on new HTTP/1.1 features
860   that are not safely interpreted by earlier HTTP/1.0 recipients.
863   The interpretation of an HTTP message header field does not change
864   between minor versions of the same major version, though the default
865   behavior of a recipient in the absence of such a field can change.
866   Unless specified otherwise, header fields defined in HTTP/1.1 are
867   defined for all versions of HTTP/1.x.  The most popular example of
868   this is the Host header field, which was introduced during the
869   standardization process of HTTP/1.1 and widely deployed for HTTP/1.0
870   requests out of necessity.
873   Likewise, new header fields can be defined such that, when they are
874   understood by a recipient, they might override or enhance the
875   interpretation of previously defined header fields.  When an
876   implementation receives an unrecognized header field, the recipient
877   &MUST; ignore that header field for local processing regardless of
878   the message's HTTP version.  An unrecognized header field received
879   by a proxy &MUST; be forwarded downstream unless the header field's
880   field-name is listed in the message's Connection header-field
881   (see <xref target="header.connection"/>).
882   These requirements allow HTTP's functionality to be enhanced without
883   requiring prior update of all compliant intermediaries.
886   Intermediaries that process HTTP messages (i.e., all intermediaries
887   other than those acting as a tunnel) &MUST; send their own HTTP-Version
888   in forwarded messages.  In other words, they &MUST-NOT; blindly
889   forward the first line of an HTTP message without ensuring that the
890   protocol version matches what the intermediary understands, and
891   is at least conditionally compliant to, for both the receiving and
892   sending of messages.  Forwarding an HTTP message without rewriting
893   the HTTP-Version might result in communication errors when downstream
894   recipients use the message sender's version to determine what features
895   are safe to use for later communication with that sender.
898   An HTTP client &SHOULD; send a request version equal to the highest
899   version for which the client is at least conditionally compliant and
900   whose major version is no higher than the highest version supported
901   by the server, if this is known.  An HTTP client &MUST-NOT; send a
902   version for which it is not at least conditionally compliant.
905   An HTTP client &MAY; send a lower request version if it is known that
906   the server incorrectly implements the HTTP specification, but only
907   after the client has attempted at least one normal request and determined
908   from the response status or header fields (e.g., Server) that the
909   server improperly handles higher request versions.
912   An HTTP server &SHOULD; send a response version equal to the highest
913   version for which the server is at least conditionally compliant and
914   whose major version is less than or equal to the one received in the
915   request.  An HTTP server &MUST-NOT; send a version for which it is not
916   at least conditionally compliant.  A server &MAY; send a 505 (HTTP
917   Version Not Supported) response if it cannot send a response using the
918   major version used in the client's request.
921   An HTTP server &MAY; send an HTTP/1.0 response to an HTTP/1.0 request
922   if it is known or suspected that the client incorrectly implements the
923   HTTP specification and is incapable of correctly processing later
924   version responses, such as when a client fails to parse the version
925   number correctly or when an intermediary is known to blindly forward
926   the HTTP-Version even when it doesn't comply with the given minor
927   version of the protocol. Such protocol downgrades &SHOULD-NOT; be
928   performed unless triggered by specific client attributes, such as when
929   one or more of the request header fields (e.g., User-Agent) uniquely
930   match the values sent by a client known to be in error.
933   The intention of HTTP's versioning design is that the major number
934   will only be incremented if an incompatible message syntax is
935   introduced, and that the minor number will only be incremented when
936   changes made to the protocol have the effect of adding to the message
937   semantics or implying additional capabilities of the sender.  However,
938   the minor version was not incremented for the changes introduced in
939   <xref target="RFC2616"/>, and this revision is specifically avoiding
940   any such changes to the protocol.
944<section title="Uniform Resource Identifiers" anchor="uri">
945<iref primary="true" item="resource"/>
947   Uniform Resource Identifiers (URIs) <xref target="RFC3986"/> are used
948   throughout HTTP as the means for identifying resources. URI references
949   are used to target requests, indicate redirects, and define relationships.
950   HTTP does not limit what a resource might be; it merely defines an interface
951   that can be used to interact with a resource via HTTP. More information on
952   the scope of URIs and resources can be found in <xref target="RFC3986"/>.
954  <x:anchor-alias value="URI-reference"/>
955  <x:anchor-alias value="absolute-URI"/>
956  <x:anchor-alias value="relative-part"/>
957  <x:anchor-alias value="authority"/>
958  <x:anchor-alias value="path-abempty"/>
959  <x:anchor-alias value="path-absolute"/>
960  <x:anchor-alias value="port"/>
961  <x:anchor-alias value="query"/>
962  <x:anchor-alias value="uri-host"/>
963  <x:anchor-alias value="partial-URI"/>
965   This specification adopts the definitions of "URI-reference",
966   "absolute-URI", "relative-part", "port", "host",
967   "path-abempty", "path-absolute", "query", and "authority" from
968   <xref target="RFC3986"/>. In addition, we define a partial-URI rule for
969   protocol elements that allow a relative URI without a fragment.
971<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="URI-reference"/><iref primary="true" item="Grammar" subitem="absolute-URI"/><iref primary="true" item="Grammar" subitem="authority"/><iref primary="true" item="Grammar" subitem="path-absolute"/><iref primary="true" item="Grammar" subitem="port"/><iref primary="true" item="Grammar" subitem="query"/><iref primary="true" item="Grammar" subitem="uri-host"/>
972  <x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in <xref target="RFC3986" x:fmt="," x:sec="4.1"/>&gt;
973  <x:ref>absolute-URI</x:ref>  = &lt;absolute-URI, defined in <xref target="RFC3986" x:fmt="," x:sec="4.3"/>&gt;
974  <x:ref>relative-part</x:ref> = &lt;relative-part, defined in <xref target="RFC3986" x:fmt="," x:sec="4.2"/>&gt;
975  <x:ref>authority</x:ref>     = &lt;authority, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2"/>&gt;
976  <x:ref>path-abempty</x:ref>  = &lt;path-abempty, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
977  <x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
978  <x:ref>port</x:ref>          = &lt;port, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.3"/>&gt;
979  <x:ref>query</x:ref>         = &lt;query, defined in <xref target="RFC3986" x:fmt="," x:sec="3.4"/>&gt;
980  <x:ref>uri-host</x:ref>      = &lt;host, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>&gt;
982  <x:ref>partial-URI</x:ref>   = relative-part [ "?" query ]
985   Each protocol element in HTTP that allows a URI reference will indicate in
986   its ABNF production whether the element allows only a URI in absolute form
987   (absolute-URI), any relative reference (relative-ref), or some other subset
988   of the URI-reference grammar. Unless otherwise indicated, URI references
989   are parsed relative to the request target (the default base URI for both
990   the request and its corresponding response).
993<section title="http URI scheme" anchor="http.uri">
994  <x:anchor-alias value="http-URI"/>
995  <iref item="http URI scheme" primary="true"/>
996  <iref item="URI scheme" subitem="http" primary="true"/>
998   The "http" URI scheme is hereby defined for the purpose of minting
999   identifiers according to their association with the hierarchical
1000   namespace governed by a potential HTTP origin server listening for
1001   TCP connections on a given port.
1002   The HTTP server is identified via the generic syntax's
1003   <x:ref>authority</x:ref> component, which includes a host
1004   identifier and optional TCP port, and the remainder of the URI is
1005   considered to be identifying data corresponding to a resource for
1006   which that server might provide an HTTP interface.
1008<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="http-URI"/>
1009  <x:ref>http-URI</x:ref> = "http:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
1012   The host identifier within an <x:ref>authority</x:ref> component is
1013   defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>.  If host is
1014   provided as an IP literal or IPv4 address, then the HTTP server is any
1015   listener on the indicated TCP port at that IP address. If host is a
1016   registered name, then that name is considered an indirect identifier
1017   and the recipient might use a name resolution service, such as DNS,
1018   to find the address of a listener for that host.
1019   The host &MUST-NOT; be empty; if an "http" URI is received with an
1020   empty host, then it &MUST; be rejected as invalid.
1021   If the port subcomponent is empty or not given, then TCP port 80 is
1022   assumed (the default reserved port for WWW services).
1025   Regardless of the form of host identifier, access to that host is not
1026   implied by the mere presence of its name or address. The host might or might
1027   not exist and, even when it does exist, might or might not be running an
1028   HTTP server or listening to the indicated port. The "http" URI scheme
1029   makes use of the delegated nature of Internet names and addresses to
1030   establish a naming authority (whatever entity has the ability to place
1031   an HTTP server at that Internet name or address) and allows that
1032   authority to determine which names are valid and how they might be used.
1035   When an "http" URI is used within a context that calls for access to the
1036   indicated resource, a client &MAY; attempt access by resolving
1037   the host to an IP address, establishing a TCP connection to that address
1038   on the indicated port, and sending an HTTP request message to the server
1039   containing the URI's identifying data as described in <xref target="request"/>.
1040   If the server responds to that request with a non-interim HTTP response
1041   message, as described in <xref target="response"/>, then that response
1042   is considered an authoritative answer to the client's request.
1045   Although HTTP is independent of the transport protocol, the "http"
1046   scheme is specific to TCP-based services because the name delegation
1047   process depends on TCP for establishing authority.
1048   An HTTP service based on some other underlying connection protocol
1049   would presumably be identified using a different URI scheme, just as
1050   the "https" scheme (below) is used for servers that require an SSL/TLS
1051   transport layer on a connection. Other protocols might also be used to
1052   provide access to "http" identified resources &mdash; it is only the
1053   authoritative interface used for mapping the namespace that is
1054   specific to TCP.
1057   The URI generic syntax for authority also includes a deprecated
1058   userinfo subcomponent (<xref target="RFC3986" x:fmt="," x:sec="3.2.1"/>)
1059   for including user authentication information in the URI.  Some
1060   implementations make use of the userinfo component for internal
1061   configuration of authentication information, such as within command
1062   invocation options, configuration files, or bookmark lists, even
1063   though such usage might expose a user identifier or password.
1064   Senders &MUST-NOT; include a userinfo subcomponent (and its "@"
1065   delimiter) when transmitting an "http" URI in a message.  Recipients
1066   of HTTP messages that contain a URI reference &SHOULD; parse for the
1067   existence of userinfo and treat its presence as an error, likely
1068   indicating that the deprecated subcomponent is being used to obscure
1069   the authority for the sake of phishing attacks.
1073<section title="https URI scheme" anchor="https.uri">
1074   <x:anchor-alias value="https-URI"/>
1075   <iref item="https URI scheme"/>
1076   <iref item="URI scheme" subitem="https"/>
1078   The "https" URI scheme is hereby defined for the purpose of minting
1079   identifiers according to their association with the hierarchical
1080   namespace governed by a potential HTTP origin server listening for
1081   SSL/TLS-secured connections on a given TCP port.
1084   All of the requirements listed above for the "http" scheme are also
1085   requirements for the "https" scheme, except that a default TCP port
1086   of 443 is assumed if the port subcomponent is empty or not given,
1087   and the TCP connection &MUST; be secured for privacy through the
1088   use of strong encryption prior to sending the first HTTP request.
1090<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="https-URI"/>
1091  <x:ref>https-URI</x:ref> = "https:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
1094   Unlike the "http" scheme, responses to "https" identified requests
1095   are never "public" and thus are ineligible for shared caching.
1096   Their default is "private" and might be further constrained via use
1097   of the Cache-Control header field.
1100   Resources made available via the "https" scheme have no shared
1101   identity with the "http" scheme even if their resource identifiers
1102   only differ by the single "s" in the scheme name.  They are
1103   different services governed by different authorities.  However,
1104   some extensions to HTTP that apply to entire host domains, such
1105   as the Cookie protocol, do allow one service to effect communication
1106   with the other services based on host domain matching.
1109   The process for authoritative access to an "https" identified
1110   resource is defined in <xref target="RFC2818"/>.
1114<section title="http and https URI Normalization and Comparison" anchor="uri.comparison">
1116   Since the "http" and "https" schemes conform to the URI generic syntax,
1117   such URIs are normalized and compared according to the algorithm defined
1118   in <xref target="RFC3986" x:fmt="," x:sec="6"/>, using the defaults
1119   described above for each scheme.
1122   If the port is equal to the default port for a scheme, the normal
1123   form is to elide the port subcomponent. Likewise, an empty path
1124   component is equivalent to an absolute path of "/", so the normal
1125   form is to provide a path of "/" instead. The scheme and host
1126   are case-insensitive and normally provided in lowercase; all
1127   other components are compared in a case-sensitive manner.
1128   Characters other than those in the "reserved" set are equivalent
1129   to their percent-encoded octets (see <xref target="RFC3986"
1130   x:fmt="," x:sec="2.1"/>): the normal form is to not encode them.
1133   For example, the following three URIs are equivalent:
1135<figure><artwork type="example">
1141   <cref anchor="TODO-not-here" source="roy">This paragraph does not belong here.</cref>
1142   If path-abempty is the empty string (i.e., there is no slash "/"
1143   path separator following the authority), then the "http" URI
1144   &MUST; be given as "/" when
1145   used as a request-target (<xref target="request-target"/>). If a proxy
1146   receives a host name which is not a fully qualified domain name, it
1147   &MAY; add its domain to the host name it received. If a proxy receives
1148   a fully qualified domain name, the proxy &MUST-NOT; change the host
1149   name.
1155<section title="HTTP Message" anchor="http.message">
1156<x:anchor-alias value="generic-message"/>
1157<x:anchor-alias value="message.types"/>
1158<x:anchor-alias value="HTTP-message"/>
1159<x:anchor-alias value="start-line"/>
1160<iref item="header section"/>
1161<iref item="headers"/>
1162<iref item="header field"/>
1164   All HTTP/1.1 messages consist of a start-line followed by a sequence of
1165   characters in a format similar to the Internet Message Format
1166   <xref target="RFC5322"/>: zero or more header fields (collectively
1167   referred to as the "headers" or the "header section"), an empty line
1168   indicating the end of the header section, and an optional message-body.
1171   An HTTP message can either be a request from client to server or a
1172   response from server to client.  Syntactically, the two types of message
1173   differ only in the start-line, which is either a Request-Line (for requests)
1174   or a Status-Line (for responses), and in the algorithm for determining
1175   the length of the message-body (<xref target="message.body"/>).
1176   In theory, a client could receive requests and a server could receive
1177   responses, distinguishing them by their different start-line formats,
1178   but in practice servers are implemented to only expect a request
1179   (a response is interpreted as an unknown or invalid request method)
1180   and clients are implemented to only expect a response.
1182<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-message"/>
1183  <x:ref>HTTP-message</x:ref>    = <x:ref>start-line</x:ref>
1184                    *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )
1185                    <x:ref>CRLF</x:ref>
1186                    [ <x:ref>message-body</x:ref> ]
1187  <x:ref>start-line</x:ref>      = <x:ref>Request-Line</x:ref> / <x:ref>Status-Line</x:ref>
1190   Whitespace (WSP) &MUST-NOT; be sent between the start-line and the first
1191   header field. The presence of whitespace might be an attempt to trick a
1192   noncompliant implementation of HTTP into ignoring that field or processing
1193   the next line as a new request, either of which might result in security
1194   issues when implementations within the request chain interpret the
1195   same message differently. HTTP/1.1 servers &MUST; reject such a message
1196   with a 400 (Bad Request) response.
1199<section title="Message Parsing Robustness" anchor="message.robustness">
1201   In the interest of robustness, servers &SHOULD; ignore at least one
1202   empty line received where a Request-Line is expected. In other words, if
1203   the server is reading the protocol stream at the beginning of a
1204   message and receives a CRLF first, it &SHOULD; ignore the CRLF.
1207   Some old HTTP/1.0 client implementations generate an extra CRLF
1208   after a POST request as a lame workaround for some early server
1209   applications that failed to read message-body content that was
1210   not terminated by a line-ending. An HTTP/1.1 client &MUST-NOT;
1211   preface or follow a request with an extra CRLF.  If terminating
1212   the request message-body with a line-ending is desired, then the
1213   client &MUST; include the terminating CRLF octets as part of the
1214   message-body length.
1217   The normal procedure for parsing an HTTP message is to read the
1218   start-line into a structure, read each header field into a hash
1219   table by field name until the empty line, and then use the parsed
1220   data to determine if a message-body is expected.  If a message-body
1221   has been indicated, then it is read as a stream until an amount
1222   of octets equal to the message-body length is read or the connection
1223   is closed.  Care must be taken to parse an HTTP message as a sequence
1224   of octets in an encoding that is a superset of US-ASCII.  Attempting
1225   to parse HTTP as a stream of Unicode characters in a character encoding
1226   like UTF-16 might introduce security flaws due to the differing ways
1227   that such parsers interpret invalid characters.
1230   HTTP allows the set of defined header fields to be extended without
1231   changing the protocol version (see <xref target="header.field.registration"/>).
1232   Unrecognized header fields &MUST; be forwarded by a proxy unless the
1233   proxy is specifically configured to block or otherwise transform such
1234   fields.  Unrecognized header fields &SHOULD; be ignored by other recipients.
1238<section title="Header Fields" anchor="header.fields">
1239  <x:anchor-alias value="header-field"/>
1240  <x:anchor-alias value="field-content"/>
1241  <x:anchor-alias value="field-name"/>
1242  <x:anchor-alias value="field-value"/>
1243  <x:anchor-alias value="OWS"/>
1245   Each HTTP header field consists of a case-insensitive field name
1246   followed by a colon (":"), optional whitespace, and the field value.
1248<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="header-field"/><iref primary="true" item="Grammar" subitem="field-name"/><iref primary="true" item="Grammar" subitem="field-value"/><iref primary="true" item="Grammar" subitem="field-content"/>
1249  <x:ref>header-field</x:ref>   = <x:ref>field-name</x:ref> ":" <x:ref>OWS</x:ref> [ <x:ref>field-value</x:ref> ] <x:ref>OWS</x:ref>
1250  <x:ref>field-name</x:ref>     = <x:ref>token</x:ref>
1251  <x:ref>field-value</x:ref>    = *( <x:ref>field-content</x:ref> / <x:ref>OWS</x:ref> )
1252  <x:ref>field-content</x:ref>  = *( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1255   No whitespace is allowed between the header field name and colon. For
1256   security reasons, any request message received containing such whitespace
1257   &MUST; be rejected with a response code of 400 (Bad Request). A proxy
1258   &MUST; remove any such whitespace from a response message before
1259   forwarding the message downstream.
1262   A field value &MAY; be preceded by optional whitespace (OWS); a single SP is
1263   preferred. The field value does not include any leading or trailing white
1264   space: OWS occurring before the first non-whitespace character of the
1265   field value or after the last non-whitespace character of the field value
1266   is ignored and &SHOULD; be removed before further processing (as this does
1267   not change the meaning of the header field).
1270   The order in which header fields with differing field names are
1271   received is not significant. However, it is "good practice" to send
1272   header fields that contain control data first, such as Host on
1273   requests and Date on responses, so that implementations can decide
1274   when not to handle a message as early as possible.  A server &MUST;
1275   wait until the entire header section is received before interpreting
1276   a request message, since later header fields might include conditionals,
1277   authentication credentials, or deliberately misleading duplicate
1278   header fields that would impact request processing.
1281   Multiple header fields with the same field name &MUST-NOT; be
1282   sent in a message unless the entire field value for that
1283   header field is defined as a comma-separated list [i.e., #(values)].
1284   Multiple header fields with the same field name can be combined into
1285   one "field-name: field-value" pair, without changing the semantics of the
1286   message, by appending each subsequent field value to the combined
1287   field value in order, separated by a comma. The order in which
1288   header fields with the same field name are received is therefore
1289   significant to the interpretation of the combined field value;
1290   a proxy &MUST-NOT; change the order of these field values when
1291   forwarding a message.
1294  <t>
1295   <x:h>Note:</x:h> The "Set-Cookie" header field as implemented in
1296   practice can occur multiple times, but does not use the list syntax, and
1297   thus cannot be combined into a single line (<xref target="draft-ietf-httpstate-cookie"/>). (See Appendix A.2.3 of <xref target="Kri2001"/>
1298   for details.) Also note that the Set-Cookie2 header field specified in
1299   <xref target="RFC2965"/> does not share this problem.
1300  </t>
1303   Historically, HTTP header field values could be extended over multiple
1304   lines by preceding each extra line with at least one space or horizontal
1305   tab character (line folding). This specification deprecates such line
1306   folding except within the message/http media type
1307   (<xref target=""/>).
1308   HTTP/1.1 senders &MUST-NOT; produce messages that include line folding
1309   (i.e., that contain any field-content that matches the obs-fold rule) unless
1310   the message is intended for packaging within the message/http media type.
1311   HTTP/1.1 recipients &SHOULD; accept line folding and replace any embedded
1312   obs-fold whitespace with a single SP prior to interpreting the field value
1313   or forwarding the message downstream.
1316   Historically, HTTP has allowed field content with text in the ISO-8859-1
1317   <xref target="ISO-8859-1"/> character encoding and supported other
1318   character sets only through use of <xref target="RFC2047"/> encoding.
1319   In practice, most HTTP header field values use only a subset of the
1320   US-ASCII character encoding <xref target="USASCII"/>. Newly defined
1321   header fields &SHOULD; limit their field values to US-ASCII characters.
1322   Recipients &SHOULD; treat other (obs-text) octets in field content as
1323   opaque data.
1325<t anchor="rule.comment">
1326  <x:anchor-alias value="comment"/>
1327  <x:anchor-alias value="ctext"/>
1328   Comments can be included in some HTTP header fields by surrounding
1329   the comment text with parentheses. Comments are only allowed in
1330   fields containing "comment" as part of their field value definition.
1332<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="comment"/><iref primary="true" item="Grammar" subitem="ctext"/>
1333  <x:ref>comment</x:ref>        = "(" *( <x:ref>ctext</x:ref> / <x:ref>quoted-cpair</x:ref> / <x:ref>comment</x:ref> ) ")"
1334  <x:ref>ctext</x:ref>          = <x:ref>OWS</x:ref> / %x21-27 / %x2A-5B / %x5D-7E / <x:ref>obs-text</x:ref>
1335                 ; <x:ref>OWS</x:ref> / &lt;<x:ref>VCHAR</x:ref> except "(", ")", and "\"&gt; / <x:ref>obs-text</x:ref>
1337<t anchor="rule.quoted-cpair">
1338  <x:anchor-alias value="quoted-cpair"/>
1339   The backslash character ("\") can be used as a single-character
1340   quoting mechanism within comment constructs:
1342<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-cpair"/>
1343  <x:ref>quoted-cpair</x:ref>    = "\" ( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1346   Producers &SHOULD-NOT; escape characters that do not require escaping
1347   (i.e., other than the backslash character "\" and the parentheses "(" and
1348   ")").
1352<section title="Message Body" anchor="message.body">
1353  <x:anchor-alias value="message-body"/>
1355   The message-body (if any) of an HTTP message is used to carry the
1356   payload body associated with the request or response.
1358<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="message-body"/>
1359  <x:ref>message-body</x:ref> = *OCTET
1362   The message-body differs from the payload body only when a transfer-coding
1363   has been applied, as indicated by the Transfer-Encoding header field
1364   (<xref target="header.transfer-encoding"/>).  If more than one
1365   Transfer-Encoding header field is present in a message, the multiple
1366   field-values &MUST; be combined into one field-value, according to the
1367   algorithm defined in <xref target="header.fields"/>, before determining
1368   the message-body length.
1371   When one or more transfer-codings are applied to a payload in order to
1372   form the message-body, the Transfer-Encoding header field &MUST; contain
1373   the list of transfer-codings applied. Transfer-Encoding is a property of
1374   the message, not of the payload, and thus &MAY; be added or removed by
1375   any implementation along the request/response chain under the constraints
1376   found in <xref target="transfer.codings"/>.
1379   If a message is received that has multiple Content-Length header fields
1380   (<xref target="header.content-length"/>) with field-values consisting
1381   of the same decimal value, or a single Content-Length header field with
1382   a field value containing a list of identical decimal values (e.g.,
1383   "Content-Length: 42, 42"), indicating that duplicate Content-Length
1384   header fields have been generated or combined by an upstream message
1385   processor, then the recipient &MUST; replace the duplicated fields or
1386   field-values with a single valid Content-Length field containing that
1387   decimal value prior to determining the message-body length.
1390   The rules for when a message-body is allowed in a message differ for
1391   requests and responses.
1394   The presence of a message-body in a request is signaled by the
1395   inclusion of a Content-Length or Transfer-Encoding header field in
1396   the request's header fields, even if the request method does not
1397   define any use for a message-body.  This allows the request
1398   message framing algorithm to be independent of method semantics.
1401   For response messages, whether or not a message-body is included with
1402   a message is dependent on both the request method and the response
1403   status code (<xref target="status.code.and.reason.phrase"/>).
1404   Responses to the HEAD request method never include a message-body
1405   because the associated response header fields (e.g., Transfer-Encoding,
1406   Content-Length, etc.) only indicate what their values would have been
1407   if the method had been GET.  All 1xx (Informational), 204 (No Content),
1408   and 304 (Not Modified) responses &MUST-NOT; include a message-body.
1409   All other responses do include a message-body, although the body
1410   &MAY; be of zero length.
1413   The length of the message-body is determined by one of the following
1414   (in order of precedence):
1417  <list style="numbers">
1418    <x:lt><t>
1419     Any response to a HEAD request and any response with a status
1420     code of 100-199, 204, or 304 is always terminated by the first
1421     empty line after the header fields, regardless of the header
1422     fields present in the message, and thus cannot contain a message-body.
1423    </t></x:lt>
1424    <x:lt><t>
1425     If a Transfer-Encoding header field is present
1426     and the "chunked" transfer-coding (<xref target="transfer.codings"/>)
1427     is the final encoding, the message-body length is determined by reading
1428     and decoding the chunked data until the transfer-coding indicates the
1429     data is complete.
1430    </t>
1431    <t>
1432     If a Transfer-Encoding header field is present in a response and the
1433     "chunked" transfer-coding is not the final encoding, the message-body
1434     length is determined by reading the connection until it is closed by
1435     the server.
1436     If a Transfer-Encoding header field is present in a request and the
1437     "chunked" transfer-coding is not the final encoding, the message-body
1438     length cannot be determined reliably; the server &MUST; respond with
1439     the 400 (Bad Request) status code and then close the connection.
1440    </t>
1441    <t>
1442     If a message is received with both a Transfer-Encoding header field
1443     and a Content-Length header field, the Transfer-Encoding overrides
1444     the Content-Length.
1445     Such a message might indicate an attempt to perform request or response
1446     smuggling (bypass of security-related checks on message routing or content)
1447     and thus ought to be handled as an error.  The provided Content-Length &MUST;
1448     be removed, prior to forwarding the message downstream, or replaced with
1449     the real message-body length after the transfer-coding is decoded.
1450    </t></x:lt>
1451    <x:lt><t>
1452     If a message is received without Transfer-Encoding and with either
1453     multiple Content-Length header fields having differing field-values or
1454     a single Content-Length header field having an invalid value, then the
1455     message framing is invalid and &MUST; be treated as an error to
1456     prevent request or response smuggling.
1457     If this is a request message, the server &MUST; respond with
1458     a 400 (Bad Request) status code and then close the connection.
1459     If this is a response message received by a proxy or gateway, the proxy
1460     or gateway &MUST; discard the received response, send a 502 (Bad Gateway)
1461     status code as its downstream response, and then close the connection.
1462     If this is a response message received by a user-agent, it &MUST; be
1463     treated as an error by discarding the message and closing the connection.
1464    </t></x:lt>
1465    <x:lt><t>
1466     If a valid Content-Length header field
1467     is present without Transfer-Encoding, its decimal value defines the
1468     message-body length in octets.  If the actual number of octets sent in
1469     the message is less than the indicated Content-Length, the recipient
1470     &MUST; consider the message to be incomplete and treat the connection
1471     as no longer usable.
1472     If the actual number of octets sent in the message is more than the indicated
1473     Content-Length, the recipient &MUST; only process the message-body up to the
1474     field value's number of octets; the remainder of the message &MUST; either
1475     be discarded or treated as the next message in a pipeline.  For the sake of
1476     robustness, a user-agent &MAY; attempt to detect and correct such an error
1477     in message framing if it is parsing the response to the last request on
1478     on a connection and the connection has been closed by the server.
1479    </t></x:lt>
1480    <x:lt><t>
1481     If this is a request message and none of the above are true, then the
1482     message-body length is zero (no message-body is present).
1483    </t></x:lt>
1484    <x:lt><t>
1485     Otherwise, this is a response message without a declared message-body
1486     length, so the message-body length is determined by the number of octets
1487     received prior to the server closing the connection.
1488    </t></x:lt>
1489  </list>
1492   Since there is no way to distinguish a successfully completed,
1493   close-delimited message from a partially-received message interrupted
1494   by network failure, implementations &SHOULD; use encoding or
1495   length-delimited messages whenever possible.  The close-delimiting
1496   feature exists primarily for backwards compatibility with HTTP/1.0.
1499   A server &MAY; reject a request that contains a message-body but
1500   not a Content-Length by responding with 411 (Length Required).
1503   Unless a transfer-coding other than "chunked" has been applied,
1504   a client that sends a request containing a message-body &SHOULD;
1505   use a valid Content-Length header field if the message-body length
1506   is known in advance, rather than the "chunked" encoding, since some
1507   existing services respond to "chunked" with a 411 (Length Required)
1508   status code even though they understand the chunked encoding.  This
1509   is typically because such services are implemented via a gateway that
1510   requires a content-length in advance of being called and the server
1511   is unable or unwilling to buffer the entire request before processing.
1514   A client that sends a request containing a message-body &MUST; include a
1515   valid Content-Length header field if it does not know the server will
1516   handle HTTP/1.1 (or later) requests; such knowledge can be in the form
1517   of specific user configuration or by remembering the version of a prior
1518   received response.
1521   Request messages that are prematurely terminated, possibly due to a
1522   cancelled connection or a server-imposed time-out exception, &MUST;
1523   result in closure of the connection; sending an HTTP/1.1 error response
1524   prior to closing the connection is &OPTIONAL;.
1525   Response messages that are prematurely terminated, usually by closure
1526   of the connection prior to receiving the expected number of octets or by
1527   failure to decode a transfer-encoded message-body, &MUST; be recorded
1528   as incomplete.  A user agent &MUST-NOT; render an incomplete response
1529   message-body as if it were complete (i.e., some indication must be given
1530   to the user that an error occurred).  Cache requirements for incomplete
1531   responses are defined in &cache-incomplete;.
1534   A server &MUST; read the entire request message-body or close
1535   the connection after sending its response, since otherwise the
1536   remaining data on a persistent connection would be misinterpreted
1537   as the next request.  Likewise,
1538   a client &MUST; read the entire response message-body if it intends
1539   to reuse the same connection for a subsequent request.  Pipelining
1540   multiple requests on a connection is described in <xref target="pipelining"/>.
1544<section title="General Header Fields" anchor="general.header.fields">
1545  <x:anchor-alias value="general-header"/>
1547   There are a few header fields which have general applicability for
1548   both request and response messages, but which do not apply to the
1549   payload being transferred. These header fields apply only to the
1550   message being transmitted.
1552<texttable align="left">
1553  <ttcol>Header Field Name</ttcol>
1554  <ttcol>Defined in...</ttcol>
1556  <c>Connection</c> <c><xref target="header.connection"/></c>
1557  <c>Date</c> <c><xref target=""/></c>
1558  <c>Pragma</c> <c>&header-pragma;</c>
1559  <c>Trailer</c> <c><xref target="header.trailer"/></c>
1560  <c>Transfer-Encoding</c> <c><xref target="header.transfer-encoding"/></c>
1561  <c>Upgrade</c> <c><xref target="header.upgrade"/></c>
1562  <c>Via</c> <c><xref target="header.via"/></c>
1563  <c>Warning</c> <c>&header-warning;</c>
1564  <c>MIME-Version</c> <c>&header-mime-version;</c>
1567   General-header field names can be extended reliably only in
1568   combination with a change in the protocol version. However, new or
1569   experimental header fields might be given the semantics of general
1570   header fields if all parties in the communication recognize them to
1571   be general-header fields.
1576<section title="Request" anchor="request">
1577  <x:anchor-alias value="Request"/>
1579   A request message from a client to a server includes, within the
1580   first line of that message, the method to be applied to the resource,
1581   the identifier of the resource, and the protocol version in use.
1583<!--                 Host                      ; should be moved here eventually -->
1584<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request"/>
1585  <x:ref>Request</x:ref>       = <x:ref>Request-Line</x:ref>              ; <xref target="request-line"/>
1586                  *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )    ; <xref target="header.fields"/>
1587                  <x:ref>CRLF</x:ref>
1588                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1591<section title="Request-Line" anchor="request-line">
1592  <x:anchor-alias value="Request-Line"/>
1594   The Request-Line begins with a method token, followed by the
1595   request-target and the protocol version, and ending with CRLF. The
1596   elements are separated by SP characters. No CR or LF is allowed
1597   except in the final CRLF sequence.
1599<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request-Line"/>
1600  <x:ref>Request-Line</x:ref>   = <x:ref>Method</x:ref> <x:ref>SP</x:ref> <x:ref>request-target</x:ref> <x:ref>SP</x:ref> <x:ref>HTTP-Version</x:ref> <x:ref>CRLF</x:ref>
1603<section title="Method" anchor="method">
1604  <x:anchor-alias value="Method"/>
1606   The Method  token indicates the method to be performed on the
1607   resource identified by the request-target. The method is case-sensitive.
1609<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Method"/>
1610  <x:ref>Method</x:ref>         = <x:ref>token</x:ref>
1614<section title="request-target" anchor="request-target">
1615  <x:anchor-alias value="request-target"/>
1617   The request-target identifies the resource upon which to apply the request.
1619<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="request-target"/>
1620  <x:ref>request-target</x:ref> = "*"
1621                 / <x:ref>absolute-URI</x:ref>
1622                 / ( <x:ref>path-absolute</x:ref> [ "?" <x:ref>query</x:ref> ] )
1623                 / <x:ref>authority</x:ref>
1626   The four options for request-target are dependent on the nature of the
1627   request.
1629<t><iref item="asterisk form (of request-target)"/>
1630   The asterisk "*" ("asterisk form") means that the request does not apply to a
1631   particular resource, but to the server itself. This is only allowed for the
1632   OPTIONS method. Thus, the only valid example is
1634<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1635OPTIONS * HTTP/1.1
1637<t><iref item="absolute-URI form (of request-target)"/>
1638   The "absolute-URI" form is &REQUIRED; when the request is being made to a
1639   proxy. The proxy is requested to forward the request or service it
1640   from a valid cache, and return the response. Note that the proxy &MAY;
1641   forward the request on to another proxy or directly to the server
1642   specified by the absolute-URI. In order to avoid request loops, a
1643   proxy &MUST; be able to recognize all of its server names, including
1644   any aliases, local variations, and the numeric IP address. An example
1645   Request-Line would be:
1647<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1648GET HTTP/1.1
1651   To allow for transition to absolute-URIs in all requests in future
1652   versions of HTTP, all HTTP/1.1 servers &MUST; accept the absolute-URI
1653   form in requests, even though HTTP/1.1 clients will only generate
1654   them in requests to proxies.
1656<t><iref item="authority form (of request-target)"/>
1657   The "authority form" is only used by the CONNECT method (&CONNECT;).
1659<t><iref item="path-absolute form (of request-target)"/>
1660   The most common form of request-target is that used to identify a
1661   resource on an origin server or gateway ("path-absolute form"). In this case the absolute
1662   path of the URI &MUST; be transmitted (see <xref target="http.uri"/>, path-absolute) as
1663   the request-target, and the network location of the URI (authority) &MUST;
1664   be transmitted in a Host header field. For example, a client wishing
1665   to retrieve the resource above directly from the origin server would
1666   create a TCP connection to port 80 of the host "" and send
1667   the lines:
1669<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1670GET /pub/WWW/TheProject.html HTTP/1.1
1674   followed by the remainder of the Request. Note that the absolute path
1675   cannot be empty; if none is present in the original URI, it &MUST; be
1676   given as "/" (the server root).
1679   If a proxy receives a request without any path in the request-target and
1680   the method specified is capable of supporting the asterisk form of
1681   request-target, then the last proxy on the request chain &MUST; forward the
1682   request with "*" as the final request-target.
1685   For example, the request
1686</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1690  would be forwarded by the proxy as
1691</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1692OPTIONS * HTTP/1.1
1696   after connecting to port 8001 of host "".
1700   The request-target is transmitted in the format specified in
1701   <xref target="http.uri"/>. If the request-target is percent-encoded
1702   (<xref target="RFC3986" x:fmt="," x:sec="2.1"/>), the origin server
1703   &MUST; decode the request-target in order to
1704   properly interpret the request. Servers &SHOULD; respond to invalid
1705   request-targets with an appropriate status code.
1708   A non-transforming proxy &MUST-NOT; rewrite the "path-absolute" part of the
1709   received request-target when forwarding it to the next inbound server,
1710   except as noted above to replace a null path-absolute with "/" or "*".
1713  <t>
1714    <x:h>Note:</x:h> The "no rewrite" rule prevents the proxy from changing the
1715    meaning of the request when the origin server is improperly using
1716    a non-reserved URI character for a reserved purpose.  Implementors
1717    need to be aware that some pre-HTTP/1.1 proxies have been known to
1718    rewrite the request-target.
1719  </t>
1722   HTTP does not place a pre-defined limit on the length of a request-target.
1723   A server &MUST; be prepared to receive URIs of unbounded length and
1724   respond with the 414 (URI Too Long) status code if the received
1725   request-target would be longer than the server wishes to handle
1726   (see &status-414;).
1729   Various ad-hoc limitations on request-target length are found in practice.
1730   It is &RECOMMENDED; that all HTTP senders and recipients support
1731   request-target lengths of 8000 or more octets.
1734  <t>
1735    <x:h>Note:</x:h> Fragments (<xref target="RFC3986" x:fmt="," x:sec="3.5"/>)
1736    are not part of the request-target and thus will not be transmitted
1737    in an HTTP request.
1738  </t>
1743<section title="The Resource Identified by a Request" anchor="">
1745   The exact resource identified by an Internet request is determined by
1746   examining both the request-target and the Host header field.
1749   An origin server that does not allow resources to differ by the
1750   requested host &MAY; ignore the Host header field value when
1751   determining the resource identified by an HTTP/1.1 request. (But see
1752   <xref target=""/>
1753   for other requirements on Host support in HTTP/1.1.)
1756   An origin server that does differentiate resources based on the host
1757   requested (sometimes referred to as virtual hosts or vanity host
1758   names) &MUST; use the following rules for determining the requested
1759   resource on an HTTP/1.1 request:
1760  <list style="numbers">
1761    <t>If request-target is an absolute-URI, the host is part of the
1762     request-target. Any Host header field value in the request &MUST; be
1763     ignored.</t>
1764    <t>If the request-target is not an absolute-URI, and the request includes
1765     a Host header field, the host is determined by the Host header
1766     field value.</t>
1767    <t>If the host as determined by rule 1 or 2 is not a valid host on
1768     the server, the response &MUST; be a 400 (Bad Request) error message.</t>
1769  </list>
1772   Recipients of an HTTP/1.0 request that lacks a Host header field &MAY;
1773   attempt to use heuristics (e.g., examination of the URI path for
1774   something unique to a particular host) in order to determine what
1775   exact resource is being requested.
1779<section title="Effective Request URI" anchor="effective.request.uri">
1780  <iref primary="true" item="effective request URI"/>
1781  <iref primary="true" item="target resource"/>
1783   HTTP requests often do not carry the absolute URI (<xref target="RFC3986" x:fmt="," x:sec="4.3"/>)
1784   for the target resource; instead, the URI needs to be inferred from the
1785   request-target, Host header field, and connection context. The result of
1786   this process is called the "effective request URI".  The "target resource"
1787   is the resource identified by the effective request URI.
1790   If the request-target is an absolute-URI, then the effective request URI is
1791   the request-target.
1794   If the request-target uses the path-absolute form or the asterisk form,
1795   and the Host header field is present, then the effective request URI is
1796   constructed by concatenating
1799  <list style="symbols">
1800    <t>
1801      the scheme name: "http" if the request was received over an insecure
1802      TCP connection, or "https" when received over a SSL/TLS-secured TCP
1803      connection,
1804    </t>
1805    <t>
1806      the character sequence "://",
1807    </t>
1808    <t>
1809      the authority component, as specified in the Host header field
1810      (<xref target=""/>), and
1811    </t>
1812    <t>
1813      the request-target obtained from the Request-Line, unless the
1814      request-target is just the asterisk "*".
1815    </t>
1816  </list>
1819   If the request-target uses the path-absolute form or the asterisk form,
1820   and the Host header field is not present, then the effective request URI is
1821   undefined.
1824   Otherwise, when request-target uses the authority form, the effective
1825   request URI is undefined.
1829   Example 1: the effective request URI for the message
1831<artwork type="example" x:indent-with="  ">
1832GET /pub/WWW/TheProject.html HTTP/1.1
1836  (received over an insecure TCP connection) is "http", plus "://", plus the
1837  authority component "", plus the request-target
1838  "/pub/WWW/TheProject.html", thus
1839  "".
1844   Example 2: the effective request URI for the message
1846<artwork type="example" x:indent-with="  ">
1847GET * HTTP/1.1
1851  (received over an SSL/TLS secured TCP connection) is "https", plus "://", plus the
1852  authority component "", thus "".
1856   Effective request URIs are compared using the rules described in
1857   <xref target="uri.comparison"/>, except that empty path components &MUST-NOT;
1858   be treated as equivalent to an absolute path of "/".
1865<section title="Response" anchor="response">
1866  <x:anchor-alias value="Response"/>
1868   After receiving and interpreting a request message, a server responds
1869   with an HTTP response message.
1871<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Response"/>
1872  <x:ref>Response</x:ref>      = <x:ref>Status-Line</x:ref>               ; <xref target="status-line"/>
1873                  *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )    ; <xref target="header.fields"/>
1874                  <x:ref>CRLF</x:ref>
1875                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1878<section title="Status-Line" anchor="status-line">
1879  <x:anchor-alias value="Status-Line"/>
1881   The first line of a Response message is the Status-Line, consisting
1882   of the protocol version followed by a numeric status code and its
1883   associated textual phrase, with each element separated by SP
1884   characters. No CR or LF is allowed except in the final CRLF sequence.
1886<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Line"/>
1887  <x:ref>Status-Line</x:ref> = <x:ref>HTTP-Version</x:ref> <x:ref>SP</x:ref> <x:ref>Status-Code</x:ref> <x:ref>SP</x:ref> <x:ref>Reason-Phrase</x:ref> <x:ref>CRLF</x:ref>
1890<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
1891  <x:anchor-alias value="Reason-Phrase"/>
1892  <x:anchor-alias value="Status-Code"/>
1894   The Status-Code element is a 3-digit integer result code of the
1895   attempt to understand and satisfy the request. These codes are fully
1896   defined in &status-codes;.  The Reason Phrase exists for the sole
1897   purpose of providing a textual description associated with the numeric
1898   status code, out of deference to earlier Internet application protocols
1899   that were more frequently used with interactive text clients.
1900   A client &SHOULD; ignore the content of the Reason Phrase.
1903   The first digit of the Status-Code defines the class of response. The
1904   last two digits do not have any categorization role. There are 5
1905   values for the first digit:
1906  <list style="symbols">
1907    <t>
1908      1xx: Informational - Request received, continuing process
1909    </t>
1910    <t>
1911      2xx: Success - The action was successfully received,
1912        understood, and accepted
1913    </t>
1914    <t>
1915      3xx: Redirection - Further action must be taken in order to
1916        complete the request
1917    </t>
1918    <t>
1919      4xx: Client Error - The request contains bad syntax or cannot
1920        be fulfilled
1921    </t>
1922    <t>
1923      5xx: Server Error - The server failed to fulfill an apparently
1924        valid request
1925    </t>
1926  </list>
1928<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Code"/><iref primary="true" item="Grammar" subitem="Reason-Phrase"/>
1929  <x:ref>Status-Code</x:ref>    = 3<x:ref>DIGIT</x:ref>
1930  <x:ref>Reason-Phrase</x:ref>  = *( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1938<section title="Protocol Parameters" anchor="protocol.parameters">
1940<section title="Date/Time Formats: Full Date" anchor="">
1941  <x:anchor-alias value="HTTP-date"/>
1943   HTTP applications have historically allowed three different formats
1944   for date/time stamps. However, the preferred format is a fixed-length subset
1945   of that defined by <xref target="RFC1123"/>:
1947<figure><artwork type="example" x:indent-with="  ">
1948Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 1123
1951   The other formats are described here only for compatibility with obsolete
1952   implementations.
1954<figure><artwork type="example" x:indent-with="  ">
1955Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
1956Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format
1959   HTTP/1.1 clients and servers that parse a date value &MUST; accept
1960   all three formats (for compatibility with HTTP/1.0), though they &MUST;
1961   only generate the RFC 1123 format for representing HTTP-date values
1962   in header fields. See <xref target="tolerant.applications"/> for further information.
1965   All HTTP date/time stamps &MUST; be represented in Greenwich Mean Time
1966   (GMT), without exception. For the purposes of HTTP, GMT is exactly
1967   equal to UTC (Coordinated Universal Time). This is indicated in the
1968   first two formats by the inclusion of "GMT" as the three-letter
1969   abbreviation for time zone, and &MUST; be assumed when reading the
1970   asctime format. HTTP-date is case sensitive and &MUST-NOT; include
1971   additional whitespace beyond that specifically included as SP in the
1972   grammar.
1974<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-date"/>
1975  <x:ref>HTTP-date</x:ref>    = <x:ref>rfc1123-date</x:ref> / <x:ref>obs-date</x:ref>
1977<t anchor="">
1978  <x:anchor-alias value="rfc1123-date"/>
1979  <x:anchor-alias value="time-of-day"/>
1980  <x:anchor-alias value="hour"/>
1981  <x:anchor-alias value="minute"/>
1982  <x:anchor-alias value="second"/>
1983  <x:anchor-alias value="day-name"/>
1984  <x:anchor-alias value="day"/>
1985  <x:anchor-alias value="month"/>
1986  <x:anchor-alias value="year"/>
1987  <x:anchor-alias value="GMT"/>
1988  Preferred format:
1990<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="rfc1123-date"/><iref primary="true" item="Grammar" subitem="date1"/><iref primary="true" item="Grammar" subitem="time-of-day"/><iref primary="true" item="Grammar" subitem="hour"/><iref primary="true" item="Grammar" subitem="minute"/><iref primary="true" item="Grammar" subitem="second"/><iref primary="true" item="Grammar" subitem="day-name"/><iref primary="true" item="Grammar" subitem="day-name-l"/><iref primary="true" item="Grammar" subitem="day"/><iref primary="true" item="Grammar" subitem="month"/><iref primary="true" item="Grammar" subitem="year"/><iref primary="true" item="Grammar" subitem="GMT"/>
1991  <x:ref>rfc1123-date</x:ref> = <x:ref>day-name</x:ref> "," <x:ref>SP</x:ref> date1 <x:ref>SP</x:ref> <x:ref>time-of-day</x:ref> <x:ref>SP</x:ref> <x:ref>GMT</x:ref>
1992  ; fixed length subset of the format defined in
1993  ; <xref target="RFC1123" x:fmt="of" x:sec="5.2.14"/>
1995  <x:ref>day-name</x:ref>     = <x:abnf-char-sequence>"Mon"</x:abnf-char-sequence> ; "Mon", case-sensitive
1996               / <x:abnf-char-sequence>"Tue"</x:abnf-char-sequence> ; "Tue", case-sensitive
1997               / <x:abnf-char-sequence>"Wed"</x:abnf-char-sequence> ; "Wed", case-sensitive
1998               / <x:abnf-char-sequence>"Thu"</x:abnf-char-sequence> ; "Thu", case-sensitive
1999               / <x:abnf-char-sequence>"Fri"</x:abnf-char-sequence> ; "Fri", case-sensitive
2000               / <x:abnf-char-sequence>"Sat"</x:abnf-char-sequence> ; "Sat", case-sensitive
2001               / <x:abnf-char-sequence>"Sun"</x:abnf-char-sequence> ; "Sun", case-sensitive
2003  <x:ref>date1</x:ref>        = <x:ref>day</x:ref> <x:ref>SP</x:ref> <x:ref>month</x:ref> <x:ref>SP</x:ref> <x:ref>year</x:ref>
2004               ; e.g., 02 Jun 1982
2006  <x:ref>day</x:ref>          = 2<x:ref>DIGIT</x:ref>
2007  <x:ref>month</x:ref>        = <x:abnf-char-sequence>"Jan"</x:abnf-char-sequence> ; "Jan", case-sensitive
2008               / <x:abnf-char-sequence>"Feb"</x:abnf-char-sequence> ; "Feb", case-sensitive
2009               / <x:abnf-char-sequence>"Mar"</x:abnf-char-sequence> ; "Mar", case-sensitive
2010               / <x:abnf-char-sequence>"Apr"</x:abnf-char-sequence> ; "Apr", case-sensitive
2011               / <x:abnf-char-sequence>"May"</x:abnf-char-sequence> ; "May", case-sensitive
2012               / <x:abnf-char-sequence>"Jun"</x:abnf-char-sequence> ; "Jun", case-sensitive
2013               / <x:abnf-char-sequence>"Jul"</x:abnf-char-sequence> ; "Jul", case-sensitive
2014               / <x:abnf-char-sequence>"Aug"</x:abnf-char-sequence> ; "Aug", case-sensitive
2015               / <x:abnf-char-sequence>"Sep"</x:abnf-char-sequence> ; "Sep", case-sensitive
2016               / <x:abnf-char-sequence>"Oct"</x:abnf-char-sequence> ; "Oct", case-sensitive
2017               / <x:abnf-char-sequence>"Nov"</x:abnf-char-sequence> ; "Nov", case-sensitive
2018               / <x:abnf-char-sequence>"Dec"</x:abnf-char-sequence> ; "Dec", case-sensitive
2019  <x:ref>year</x:ref>         = 4<x:ref>DIGIT</x:ref>
2021  <x:ref>GMT</x:ref>   = <x:abnf-char-sequence>"GMT"</x:abnf-char-sequence> ; "GMT", case-sensitive
2023  <x:ref>time-of-day</x:ref>  = <x:ref>hour</x:ref> ":" <x:ref>minute</x:ref> ":" <x:ref>second</x:ref>
2024                 ; 00:00:00 - 23:59:59
2026  <x:ref>hour</x:ref>         = 2<x:ref>DIGIT</x:ref>               
2027  <x:ref>minute</x:ref>       = 2<x:ref>DIGIT</x:ref>               
2028  <x:ref>second</x:ref>       = 2<x:ref>DIGIT</x:ref>               
2031  The semantics of <x:ref>day-name</x:ref>, <x:ref>day</x:ref>,
2032  <x:ref>month</x:ref>, <x:ref>year</x:ref>, and <x:ref>time-of-day</x:ref> are the
2033  same as those defined for the RFC 5322 constructs
2034  with the corresponding name (<xref target="RFC5322" x:fmt="," x:sec="3.3"/>).
2036<t anchor="">
2037  <x:anchor-alias value="obs-date"/>
2038  <x:anchor-alias value="rfc850-date"/>
2039  <x:anchor-alias value="asctime-date"/>
2040  <x:anchor-alias value="date1"/>
2041  <x:anchor-alias value="date2"/>
2042  <x:anchor-alias value="date3"/>
2043  <x:anchor-alias value="rfc1123-date"/>
2044  <x:anchor-alias value="day-name-l"/>
2045  Obsolete formats:
2047<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="obs-date"/>
2048  <x:ref>obs-date</x:ref>     = <x:ref>rfc850-date</x:ref> / <x:ref>asctime-date</x:ref>
2050<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="rfc850-date"/>
2051  <x:ref>rfc850-date</x:ref>  = <x:ref>day-name-l</x:ref> "," <x:ref>SP</x:ref> <x:ref>date2</x:ref> <x:ref>SP</x:ref> <x:ref>time-of-day</x:ref> <x:ref>SP</x:ref> <x:ref>GMT</x:ref>
2052  <x:ref>date2</x:ref>        = <x:ref>day</x:ref> "-" <x:ref>month</x:ref> "-" 2<x:ref>DIGIT</x:ref>
2053                 ; day-month-year (e.g., 02-Jun-82)
2055  <x:ref>day-name-l</x:ref>   = <x:abnf-char-sequence>"Monday"</x:abnf-char-sequence> ; "Monday", case-sensitive
2056         / <x:abnf-char-sequence>"Tuesday"</x:abnf-char-sequence> ; "Tuesday", case-sensitive
2057         / <x:abnf-char-sequence>"Wednesday"</x:abnf-char-sequence> ; "Wednesday", case-sensitive
2058         / <x:abnf-char-sequence>"Thursday"</x:abnf-char-sequence> ; "Thursday", case-sensitive
2059         / <x:abnf-char-sequence>"Friday"</x:abnf-char-sequence> ; "Friday", case-sensitive
2060         / <x:abnf-char-sequence>"Saturday"</x:abnf-char-sequence> ; "Saturday", case-sensitive
2061         / <x:abnf-char-sequence>"Sunday"</x:abnf-char-sequence> ; "Sunday", case-sensitive
2063<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="asctime-date"/>
2064  <x:ref>asctime-date</x:ref> = <x:ref>day-name</x:ref> <x:ref>SP</x:ref> <x:ref>date3</x:ref> <x:ref>SP</x:ref> <x:ref>time-of-day</x:ref> <x:ref>SP</x:ref> <x:ref>year</x:ref>
2065  <x:ref>date3</x:ref>        = <x:ref>month</x:ref> <x:ref>SP</x:ref> ( 2<x:ref>DIGIT</x:ref> / ( <x:ref>SP</x:ref> 1<x:ref>DIGIT</x:ref> ))
2066                 ; month day (e.g., Jun  2)
2069  <t>
2070    <x:h>Note:</x:h> Recipients of date values are encouraged to be robust in
2071    accepting date values that might have been sent by non-HTTP
2072    applications, as is sometimes the case when retrieving or posting
2073    messages via proxies/gateways to SMTP or NNTP.
2074  </t>
2077  <t>
2078    <x:h>Note:</x:h> HTTP requirements for the date/time stamp format apply only
2079    to their usage within the protocol stream. Clients and servers are
2080    not required to use these formats for user presentation, request
2081    logging, etc.
2082  </t>
2086<section title="Transfer Codings" anchor="transfer.codings">
2087  <x:anchor-alias value="transfer-coding"/>
2088  <x:anchor-alias value="transfer-extension"/>
2090   Transfer-coding values are used to indicate an encoding
2091   transformation that has been, can be, or might need to be applied to a
2092   payload body in order to ensure "safe transport" through the network.
2093   This differs from a content coding in that the transfer-coding is a
2094   property of the message rather than a property of the representation
2095   that is being transferred.
2097<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/>
2098  <x:ref>transfer-coding</x:ref>         = "chunked" ; <xref target="chunked.encoding"/>
2099                          / "compress" ; <xref target="compress.coding"/>
2100                          / "deflate" ; <xref target="deflate.coding"/>
2101                          / "gzip" ; <xref target="gzip.coding"/>
2102                          / <x:ref>transfer-extension</x:ref>
2103  <x:ref>transfer-extension</x:ref>      = <x:ref>token</x:ref> *( <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>transfer-parameter</x:ref> )
2105<t anchor="rule.parameter">
2106  <x:anchor-alias value="attribute"/>
2107  <x:anchor-alias value="transfer-parameter"/>
2108  <x:anchor-alias value="value"/>
2109   Parameters are in the form of attribute/value pairs.
2111<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-parameter"/><iref primary="true" item="Grammar" subitem="attribute"/><iref primary="true" item="Grammar" subitem="value"/><iref primary="true" item="Grammar" subitem="date2"/><iref primary="true" item="Grammar" subitem="date3"/>
2112  <x:ref>transfer-parameter</x:ref>      = <x:ref>attribute</x:ref> <x:ref>BWS</x:ref> "=" <x:ref>BWS</x:ref> <x:ref>value</x:ref>
2113  <x:ref>attribute</x:ref>               = <x:ref>token</x:ref>
2114  <x:ref>value</x:ref>                   = <x:ref>word</x:ref>
2117   All transfer-coding values are case-insensitive. HTTP/1.1 uses
2118   transfer-coding values in the TE header field (<xref target="header.te"/>) and in
2119   the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
2122   Transfer-codings are analogous to the Content-Transfer-Encoding values of
2123   MIME, which were designed to enable safe transport of binary data over a
2124   7-bit transport service (<xref target="RFC2045" x:fmt="," x:sec="6"/>).
2125   However, safe transport
2126   has a different focus for an 8bit-clean transfer protocol. In HTTP,
2127   the only unsafe characteristic of message-bodies is the difficulty in
2128   determining the exact message body length (<xref target="message.body"/>),
2129   or the desire to encrypt data over a shared transport.
2132   A server that receives a request message with a transfer-coding it does
2133   not understand &SHOULD; respond with 501 (Not Implemented) and then
2134   close the connection. A server &MUST-NOT; send transfer-codings to an HTTP/1.0
2135   client.
2138<section title="Chunked Transfer Coding" anchor="chunked.encoding">
2139  <iref item="chunked (Coding Format)"/>
2140  <iref item="Coding Format" subitem="chunked"/>
2141  <x:anchor-alias value="chunk"/>
2142  <x:anchor-alias value="Chunked-Body"/>
2143  <x:anchor-alias value="chunk-data"/>
2144  <x:anchor-alias value="chunk-ext"/>
2145  <x:anchor-alias value="chunk-ext-name"/>
2146  <x:anchor-alias value="chunk-ext-val"/>
2147  <x:anchor-alias value="chunk-size"/>
2148  <x:anchor-alias value="last-chunk"/>
2149  <x:anchor-alias value="trailer-part"/>
2150  <x:anchor-alias value="quoted-str-nf"/>
2151  <x:anchor-alias value="qdtext-nf"/>
2153   The chunked encoding modifies the body of a message in order to
2154   transfer it as a series of chunks, each with its own size indicator,
2155   followed by an &OPTIONAL; trailer containing header fields. This
2156   allows dynamically produced content to be transferred along with the
2157   information necessary for the recipient to verify that it has
2158   received the full message.
2160<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Chunked-Body"/><iref primary="true" item="Grammar" subitem="chunk"/><iref primary="true" item="Grammar" subitem="chunk-size"/><iref primary="true" item="Grammar" subitem="last-chunk"/><iref primary="true" item="Grammar" subitem="chunk-ext"/><iref primary="true" item="Grammar" subitem="chunk-ext-name"/><iref primary="true" item="Grammar" subitem="chunk-ext-val"/><iref primary="true" item="Grammar" subitem="chunk-data"/><iref primary="true" item="Grammar" subitem="trailer-part"/><iref primary="true" item="Grammar" subitem="quoted-str-nf"/><iref primary="true" item="Grammar" subitem="qdtext-nf"/>
2161  <x:ref>Chunked-Body</x:ref>   = *<x:ref>chunk</x:ref>
2162                   <x:ref>last-chunk</x:ref>
2163                   <x:ref>trailer-part</x:ref>
2164                   <x:ref>CRLF</x:ref>
2166  <x:ref>chunk</x:ref>          = <x:ref>chunk-size</x:ref> *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
2167                   <x:ref>chunk-data</x:ref> <x:ref>CRLF</x:ref>
2168  <x:ref>chunk-size</x:ref>     = 1*<x:ref>HEXDIG</x:ref>
2169  <x:ref>last-chunk</x:ref>     = 1*("0") *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
2171  <x:ref>chunk-ext</x:ref>      = *( ";" *WSP <x:ref>chunk-ext-name</x:ref>
2172                      [ "=" <x:ref>chunk-ext-val</x:ref> ] *WSP )
2173  <x:ref>chunk-ext-name</x:ref> = <x:ref>token</x:ref>
2174  <x:ref>chunk-ext-val</x:ref>  = <x:ref>token</x:ref> / <x:ref>quoted-str-nf</x:ref>
2175  <x:ref>chunk-data</x:ref>     = 1*<x:ref>OCTET</x:ref> ; a sequence of chunk-size octets
2176  <x:ref>trailer-part</x:ref>   = *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )
2178  <x:ref>quoted-str-nf</x:ref>  = <x:ref>DQUOTE</x:ref> *( <x:ref>qdtext-nf</x:ref> / <x:ref>quoted-pair</x:ref> ) <x:ref>DQUOTE</x:ref>
2179                 ; like <x:ref>quoted-string</x:ref>, but disallowing line folding
2180  <x:ref>qdtext-nf</x:ref>      = <x:ref>WSP</x:ref> / %x21 / %x23-5B / %x5D-7E / <x:ref>obs-text</x:ref>
2181                 ; <x:ref>WSP</x:ref> / &lt;<x:ref>VCHAR</x:ref> except <x:ref>DQUOTE</x:ref> and "\"&gt; / <x:ref>obs-text</x:ref>
2184   The chunk-size field is a string of hex digits indicating the size of
2185   the chunk-data in octets. The chunked encoding is ended by any chunk whose size is
2186   zero, followed by the trailer, which is terminated by an empty line.
2189   The trailer allows the sender to include additional HTTP header
2190   fields at the end of the message. The Trailer header field can be
2191   used to indicate which header fields are included in a trailer (see
2192   <xref target="header.trailer"/>).
2195   A server using chunked transfer-coding in a response &MUST-NOT; use the
2196   trailer for any header fields unless at least one of the following is
2197   true:
2198  <list style="numbers">
2199    <t>the request included a TE header field that indicates "trailers" is
2200     acceptable in the transfer-coding of the  response, as described in
2201     <xref target="header.te"/>; or,</t>
2203    <t>the trailer fields consist entirely of optional metadata, and the
2204    recipient could use the message (in a manner acceptable to the server where
2205    the field originated) without receiving it. In other words, the server that
2206    generated the header (often but not always the origin server) is willing to
2207    accept the possibility that the trailer fields might be silently discarded
2208    along the path to the client.</t>
2209  </list>
2212   This requirement prevents an interoperability failure when the
2213   message is being received by an HTTP/1.1 (or later) proxy and
2214   forwarded to an HTTP/1.0 recipient. It avoids a situation where
2215   compliance with the protocol would have necessitated a possibly
2216   infinite buffer on the proxy.
2219   A process for decoding the "chunked" transfer-coding
2220   can be represented in pseudo-code as:
2222<figure><artwork type="code">
2223  length := 0
2224  read chunk-size, chunk-ext (if any) and CRLF
2225  while (chunk-size &gt; 0) {
2226     read chunk-data and CRLF
2227     append chunk-data to decoded-body
2228     length := length + chunk-size
2229     read chunk-size and CRLF
2230  }
2231  read header-field
2232  while (header-field not empty) {
2233     append header-field to existing header fields
2234     read header-field
2235  }
2236  Content-Length := length
2237  Remove "chunked" from Transfer-Encoding
2240   All HTTP/1.1 applications &MUST; be able to receive and decode the
2241   "chunked" transfer-coding and &MUST; ignore chunk-ext extensions
2242   they do not understand.
2245   Since "chunked" is the only transfer-coding required to be understood
2246   by HTTP/1.1 recipients, it plays a crucial role in delimiting messages
2247   on a persistent connection.  Whenever a transfer-coding is applied to
2248   a payload body in a request, the final transfer-coding applied &MUST;
2249   be "chunked".  If a transfer-coding is applied to a response payload
2250   body, then either the final transfer-coding applied &MUST; be "chunked"
2251   or the message &MUST; be terminated by closing the connection. When the
2252   "chunked" transfer-coding is used, it &MUST; be the last transfer-coding
2253   applied to form the message-body. The "chunked" transfer-coding &MUST-NOT;
2254   be applied more than once in a message-body.
2258<section title="Compression Codings" anchor="compression.codings">
2260   The codings defined below can be used to compress the payload of a
2261   message.
2264   <x:h>Note:</x:h> Use of program names for the identification of encoding formats
2265   is not desirable and is discouraged for future encodings. Their
2266   use here is representative of historical practice, not good
2267   design.
2270   <x:h>Note:</x:h> For compatibility with previous implementations of HTTP,
2271   applications &SHOULD; consider "x-gzip" and "x-compress" to be
2272   equivalent to "gzip" and "compress" respectively.
2275<section title="Compress Coding" anchor="compress.coding">
2276<iref item="compress (Coding Format)"/>
2277<iref item="Coding Format" subitem="compress"/>
2279   The "compress" format is produced by the common UNIX file compression
2280   program "compress". This format is an adaptive Lempel-Ziv-Welch
2281   coding (LZW).
2285<section title="Deflate Coding" anchor="deflate.coding">
2286<iref item="deflate (Coding Format)"/>
2287<iref item="Coding Format" subitem="deflate"/>
2289   The "deflate" format is defined as the "deflate" compression mechanism
2290   (described in <xref target="RFC1951"/>) used inside the "zlib"
2291   data format (<xref target="RFC1950"/>).
2294  <t>
2295    <x:h>Note:</x:h> Some incorrect implementations send the "deflate"
2296    compressed data without the zlib wrapper.
2297   </t>
2301<section title="Gzip Coding" anchor="gzip.coding">
2302<iref item="gzip (Coding Format)"/>
2303<iref item="Coding Format" subitem="gzip"/>
2305   The "gzip" format is produced by the file compression program
2306   "gzip" (GNU zip), as described in <xref target="RFC1952"/>. This format is a
2307   Lempel-Ziv coding (LZ77) with a 32 bit CRC.
2313<section title="Transfer Coding Registry" anchor="transfer.coding.registry">
2315   The HTTP Transfer Coding Registry defines the name space for the transfer
2316   coding names.
2319   Registrations &MUST; include the following fields:
2320   <list style="symbols">
2321     <t>Name</t>
2322     <t>Description</t>
2323     <t>Pointer to specification text</t>
2324   </list>
2327   Names of transfer codings &MUST-NOT; overlap with names of content codings
2328   (&content-codings;), unless the encoding transformation is identical (as it
2329   is the case for the compression codings defined in
2330   <xref target="compression.codings"/>).
2333   Values to be added to this name space require a specification
2334   (see "Specification Required" in <xref target="RFC5226" x:fmt="of" x:sec="4.1"/>), and &MUST;
2335   conform to the purpose of transfer coding defined in this section.
2338   The registry itself is maintained at
2339   <eref target=""/>.
2344<section title="Product Tokens" anchor="product.tokens">
2345  <x:anchor-alias value="product"/>
2346  <x:anchor-alias value="product-version"/>
2348   Product tokens are used to allow communicating applications to
2349   identify themselves by software name and version. Most fields using
2350   product tokens also allow sub-products which form a significant part
2351   of the application to be listed, separated by whitespace. By
2352   convention, the products are listed in order of their significance
2353   for identifying the application.
2355<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/>
2356  <x:ref>product</x:ref>         = <x:ref>token</x:ref> ["/" <x:ref>product-version</x:ref>]
2357  <x:ref>product-version</x:ref> = <x:ref>token</x:ref>
2360   Examples:
2362<figure><artwork type="example">
2363  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
2364  Server: Apache/0.8.4
2367   Product tokens &SHOULD; be short and to the point. They &MUST-NOT; be
2368   used for advertising or other non-essential information. Although any
2369   token character &MAY; appear in a product-version, this token &SHOULD;
2370   only be used for a version identifier (i.e., successive versions of
2371   the same product &SHOULD; only differ in the product-version portion of
2372   the product value).
2376<section title="Quality Values" anchor="quality.values">
2377  <x:anchor-alias value="qvalue"/>
2379   Both transfer codings (TE request header field, <xref target="header.te"/>)
2380   and content negotiation (&content.negotiation;) use short "floating point"
2381   numbers to indicate the relative importance ("weight") of various
2382   negotiable parameters.  A weight is normalized to a real number in
2383   the range 0 through 1, where 0 is the minimum and 1 the maximum
2384   value. If a parameter has a quality value of 0, then content with
2385   this parameter is "not acceptable" for the client. HTTP/1.1
2386   applications &MUST-NOT; generate more than three digits after the
2387   decimal point. User configuration of these values &SHOULD; also be
2388   limited in this fashion.
2390<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="qvalue"/>
2391  <x:ref>qvalue</x:ref>         = ( "0" [ "." 0*3<x:ref>DIGIT</x:ref> ] )
2392                 / ( "1" [ "." 0*3("0") ] )
2395  <t>
2396     <x:h>Note:</x:h> "Quality values" is a misnomer, since these values merely represent
2397     relative degradation in desired quality.
2398  </t>
2404<section title="Connections" anchor="connections">
2406<section title="Persistent Connections" anchor="persistent.connections">
2408<section title="Purpose" anchor="persistent.purpose">
2410   Prior to persistent connections, a separate TCP connection was
2411   established to fetch each URL, increasing the load on HTTP servers
2412   and causing congestion on the Internet. The use of inline images and
2413   other associated data often requires a client to make multiple
2414   requests of the same server in a short amount of time. Analysis of
2415   these performance problems and results from a prototype
2416   implementation are available <xref target="Pad1995"/> <xref target="Spe"/>. Implementation experience and
2417   measurements of actual HTTP/1.1 implementations show good
2418   results <xref target="Nie1997"/>. Alternatives have also been explored, for example,
2419   T/TCP <xref target="Tou1998"/>.
2422   Persistent HTTP connections have a number of advantages:
2423  <list style="symbols">
2424      <t>
2425        By opening and closing fewer TCP connections, CPU time is saved
2426        in routers and hosts (clients, servers, proxies, gateways,
2427        tunnels, or caches), and memory used for TCP protocol control
2428        blocks can be saved in hosts.
2429      </t>
2430      <t>
2431        HTTP requests and responses can be pipelined on a connection.
2432        Pipelining allows a client to make multiple requests without
2433        waiting for each response, allowing a single TCP connection to
2434        be used much more efficiently, with much lower elapsed time.
2435      </t>
2436      <t>
2437        Network congestion is reduced by reducing the number of packets
2438        caused by TCP opens, and by allowing TCP sufficient time to
2439        determine the congestion state of the network.
2440      </t>
2441      <t>
2442        Latency on subsequent requests is reduced since there is no time
2443        spent in TCP's connection opening handshake.
2444      </t>
2445      <t>
2446        HTTP can evolve more gracefully, since errors can be reported
2447        without the penalty of closing the TCP connection. Clients using
2448        future versions of HTTP might optimistically try a new feature,
2449        but if communicating with an older server, retry with old
2450        semantics after an error is reported.
2451      </t>
2452    </list>
2455   HTTP implementations &SHOULD; implement persistent connections.
2459<section title="Overall Operation" anchor="persistent.overall">
2461   A significant difference between HTTP/1.1 and earlier versions of
2462   HTTP is that persistent connections are the default behavior of any
2463   HTTP connection. That is, unless otherwise indicated, the client
2464   &SHOULD; assume that the server will maintain a persistent connection,
2465   even after error responses from the server.
2468   Persistent connections provide a mechanism by which a client and a
2469   server can signal the close of a TCP connection. This signaling takes
2470   place using the Connection header field (<xref target="header.connection"/>). Once a close
2471   has been signaled, the client &MUST-NOT; send any more requests on that
2472   connection.
2475<section title="Negotiation" anchor="persistent.negotiation">
2477   An HTTP/1.1 server &MAY; assume that a HTTP/1.1 client intends to
2478   maintain a persistent connection unless a Connection header field including
2479   the connection-token "close" was sent in the request. If the server
2480   chooses to close the connection immediately after sending the
2481   response, it &SHOULD; send a Connection header field including the
2482   connection-token "close".
2485   An HTTP/1.1 client &MAY; expect a connection to remain open, but would
2486   decide to keep it open based on whether the response from a server
2487   contains a Connection header field with the connection-token close. In case
2488   the client does not want to maintain a connection for more than that
2489   request, it &SHOULD; send a Connection header field including the
2490   connection-token close.
2493   If either the client or the server sends the close token in the
2494   Connection header field, that request becomes the last one for the
2495   connection.
2498   Clients and servers &SHOULD-NOT;  assume that a persistent connection is
2499   maintained for HTTP versions less than 1.1 unless it is explicitly
2500   signaled. See <xref target="compatibility.with.http.1.0.persistent.connections"/> for more information on backward
2501   compatibility with HTTP/1.0 clients.
2504   In order to remain persistent, all messages on the connection &MUST;
2505   have a self-defined message length (i.e., one not defined by closure
2506   of the connection), as described in <xref target="message.body"/>.
2510<section title="Pipelining" anchor="pipelining">
2512   A client that supports persistent connections &MAY; "pipeline" its
2513   requests (i.e., send multiple requests without waiting for each
2514   response). A server &MUST; send its responses to those requests in the
2515   same order that the requests were received.
2518   Clients which assume persistent connections and pipeline immediately
2519   after connection establishment &SHOULD; be prepared to retry their
2520   connection if the first pipelined attempt fails. If a client does
2521   such a retry, it &MUST-NOT; pipeline before it knows the connection is
2522   persistent. Clients &MUST; also be prepared to resend their requests if
2523   the server closes the connection before sending all of the
2524   corresponding responses.
2527   Clients &SHOULD-NOT;  pipeline requests using non-idempotent methods or
2528   non-idempotent sequences of methods (see &idempotent-methods;). Otherwise, a
2529   premature termination of the transport connection could lead to
2530   indeterminate results. A client wishing to send a non-idempotent
2531   request &SHOULD; wait to send that request until it has received the
2532   response status line for the previous request.
2537<section title="Proxy Servers" anchor="persistent.proxy">
2539   It is especially important that proxies correctly implement the
2540   properties of the Connection header field as specified in <xref target="header.connection"/>.
2543   The proxy server &MUST; signal persistent connections separately with
2544   its clients and the origin servers (or other proxy servers) that it
2545   connects to. Each persistent connection applies to only one transport
2546   link.
2549   A proxy server &MUST-NOT; establish a HTTP/1.1 persistent connection
2550   with an HTTP/1.0 client (but see <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>
2551   for information and discussion of the problems with the Keep-Alive header field
2552   implemented by many HTTP/1.0 clients).
2555<section title="End-to-end and Hop-by-hop Header Fields" anchor="end-to-end.and.hop-by-hop.header-fields">
2557  <cref anchor="TODO-end-to-end" source="jre">
2558    Restored from <eref target=""/>.
2559    See also <eref target=""/>.
2560  </cref>
2563   For the purpose of defining the behavior of caches and non-caching
2564   proxies, we divide HTTP header fields into two categories:
2565  <list style="symbols">
2566      <t>End-to-end header fields, which are  transmitted to the ultimate
2567        recipient of a request or response. End-to-end header fields in
2568        responses MUST be stored as part of a cache entry and &MUST; be
2569        transmitted in any response formed from a cache entry.</t>
2571      <t>Hop-by-hop header fields, which are meaningful only for a single
2572        transport-level connection, and are not stored by caches or
2573        forwarded by proxies.</t>
2574  </list>
2577   The following HTTP/1.1 header fields are hop-by-hop header fields:
2578  <list style="symbols">
2579      <t>Connection</t>
2580      <t>Keep-Alive</t>
2581      <t>Proxy-Authenticate</t>
2582      <t>Proxy-Authorization</t>
2583      <t>TE</t>
2584      <t>Trailer</t>
2585      <t>Transfer-Encoding</t>
2586      <t>Upgrade</t>
2587  </list>
2590   All other header fields defined by HTTP/1.1 are end-to-end header fields.
2593   Other hop-by-hop header fields &MUST; be listed in a Connection header field
2594   (<xref target="header.connection"/>).
2598<section title="Non-modifiable Header Fields" anchor="non-modifiable.header-fields">
2600  <cref anchor="TODO-non-mod-headers" source="jre">
2601    Restored from <eref target=""/>.
2602    See also <eref target=""/>.
2603  </cref>
2606   Some features of HTTP/1.1, such as Digest Authentication, depend on the
2607   value of certain end-to-end header fields. A non-transforming proxy &SHOULD-NOT;
2608   modify an end-to-end header field unless the definition of that header field requires
2609   or specifically allows that.
2612   A non-transforming proxy &MUST-NOT; modify any of the following fields in a
2613   request or response, and it &MUST-NOT; add any of these fields if not
2614   already present:
2615  <list style="symbols">
2616      <t>Content-Location</t>
2617      <t>Content-MD5</t>
2618      <t>ETag</t>
2619      <t>Last-Modified</t>
2620  </list>
2623   A non-transforming proxy &MUST-NOT; modify any of the following fields in a
2624   response:
2625  <list style="symbols">
2626    <t>Expires</t>
2627  </list>
2630   but it &MAY; add any of these fields if not already present. If an
2631   Expires header field is added, it &MUST; be given a field-value identical to
2632   that of the Date header field in that response.
2635   A proxy &MUST-NOT; modify or add any of the following fields in a
2636   message that contains the no-transform cache-control directive, or in
2637   any request:
2638  <list style="symbols">
2639    <t>Content-Encoding</t>
2640    <t>Content-Range</t>
2641    <t>Content-Type</t>
2642  </list>
2645   A transforming proxy &MAY; modify or add these fields to a message
2646   that does not include no-transform, but if it does so, it &MUST; add a
2647   Warning 214 (Transformation applied) if one does not already appear
2648   in the message (see &header-warning;).
2651  <t>
2652    <x:h>Warning:</x:h> Unnecessary modification of end-to-end header fields might
2653    cause authentication failures if stronger authentication
2654    mechanisms are introduced in later versions of HTTP. Such
2655    authentication mechanisms &MAY; rely on the values of header fields
2656    not listed here.
2657  </t>
2660   A non-transforming proxy &MUST; preserve the message payload (&payload;),
2661   though it &MAY; change the message-body through application or removal
2662   of a transfer-coding (<xref target="transfer.codings"/>).
2668<section title="Practical Considerations" anchor="persistent.practical">
2670   Servers will usually have some time-out value beyond which they will
2671   no longer maintain an inactive connection. Proxy servers might make
2672   this a higher value since it is likely that the client will be making
2673   more connections through the same server. The use of persistent
2674   connections places no requirements on the length (or existence) of
2675   this time-out for either the client or the server.
2678   When a client or server wishes to time-out it &SHOULD; issue a graceful
2679   close on the transport connection. Clients and servers &SHOULD; both
2680   constantly watch for the other side of the transport close, and
2681   respond to it as appropriate. If a client or server does not detect
2682   the other side's close promptly it could cause unnecessary resource
2683   drain on the network.
2686   A client, server, or proxy &MAY; close the transport connection at any
2687   time. For example, a client might have started to send a new request
2688   at the same time that the server has decided to close the "idle"
2689   connection. From the server's point of view, the connection is being
2690   closed while it was idle, but from the client's point of view, a
2691   request is in progress.
2694   This means that clients, servers, and proxies &MUST; be able to recover
2695   from asynchronous close events. Client software &SHOULD; reopen the
2696   transport connection and retransmit the aborted sequence of requests
2697   without user interaction so long as the request sequence is
2698   idempotent (see &idempotent-methods;). Non-idempotent methods or sequences
2699   &MUST-NOT; be automatically retried, although user agents &MAY; offer a
2700   human operator the choice of retrying the request(s). Confirmation by
2701   user-agent software with semantic understanding of the application
2702   &MAY; substitute for user confirmation. The automatic retry &SHOULD-NOT;
2703   be repeated if the second sequence of requests fails.
2706   Servers &SHOULD; always respond to at least one request per connection,
2707   if at all possible. Servers &SHOULD-NOT;  close a connection in the
2708   middle of transmitting a response, unless a network or client failure
2709   is suspected.
2712   Clients (including proxies) &SHOULD; limit the number of simultaneous
2713   connections that they maintain to a given server (including proxies).
2716   Previous revisions of HTTP gave a specific number of connections as a
2717   ceiling, but this was found to be impractical for many applications. As a
2718   result, this specification does not mandate a particular maximum number of
2719   connections, but instead encourages clients to be conservative when opening
2720   multiple connections.
2723   In particular, while using multiple connections avoids the "head-of-line
2724   blocking" problem (whereby a request that takes significant server-side
2725   processing and/or has a large payload can block subsequent requests on the
2726   same connection), each connection used consumes server resources (sometimes
2727   significantly), and furthermore using multiple connections can cause
2728   undesirable side effects in congested networks.
2731   Note that servers might reject traffic that they deem abusive, including an
2732   excessive number of connections from a client.
2737<section title="Message Transmission Requirements" anchor="message.transmission.requirements">
2739<section title="Persistent Connections and Flow Control" anchor="persistent.flow">
2741   HTTP/1.1 servers &SHOULD; maintain persistent connections and use TCP's
2742   flow control mechanisms to resolve temporary overloads, rather than
2743   terminating connections with the expectation that clients will retry.
2744   The latter technique can exacerbate network congestion.
2748<section title="Monitoring Connections for Error Status Messages" anchor="persistent.monitor">
2750   An HTTP/1.1 (or later) client sending a message-body &SHOULD; monitor
2751   the network connection for an error status code while it is transmitting
2752   the request. If the client sees an error status code, it &SHOULD;
2753   immediately cease transmitting the body. If the body is being sent
2754   using a "chunked" encoding (<xref target="transfer.codings"/>), a zero length chunk and
2755   empty trailer &MAY; be used to prematurely mark the end of the message.
2756   If the body was preceded by a Content-Length header field, the client &MUST;
2757   close the connection.
2761<section title="Use of the 100 (Continue) Status" anchor="use.of.the.100.status">
2763   The purpose of the 100 (Continue) status code (see &status-100;) is to
2764   allow a client that is sending a request message with a request body
2765   to determine if the origin server is willing to accept the request
2766   (based on the request header fields) before the client sends the request
2767   body. In some cases, it might either be inappropriate or highly
2768   inefficient for the client to send the body if the server will reject
2769   the message without looking at the body.
2772   Requirements for HTTP/1.1 clients:
2773  <list style="symbols">
2774    <t>
2775        If a client will wait for a 100 (Continue) response before
2776        sending the request body, it &MUST; send an Expect request-header
2777        field (&header-expect;) with the "100-continue" expectation.
2778    </t>
2779    <t>
2780        A client &MUST-NOT; send an Expect request-header field (&header-expect;)
2781        with the "100-continue" expectation if it does not intend
2782        to send a request body.
2783    </t>
2784  </list>
2787   Because of the presence of older implementations, the protocol allows
2788   ambiguous situations in which a client might send "Expect: 100-continue"
2789   without receiving either a 417 (Expectation Failed)
2790   or a 100 (Continue) status code. Therefore, when a client sends this
2791   header field to an origin server (possibly via a proxy) from which it
2792   has never seen a 100 (Continue) status code, the client &SHOULD-NOT; 
2793   wait for an indefinite period before sending the request body.
2796   Requirements for HTTP/1.1 origin servers:
2797  <list style="symbols">
2798    <t> Upon receiving a request which includes an Expect request-header
2799        field with the "100-continue" expectation, an origin server &MUST;
2800        either respond with 100 (Continue) status code and continue to read
2801        from the input stream, or respond with a final status code. The
2802        origin server &MUST-NOT; wait for the request body before sending
2803        the 100 (Continue) response. If it responds with a final status
2804        code, it &MAY; close the transport connection or it &MAY; continue
2805        to read and discard the rest of the request.  It &MUST-NOT;
2806        perform the requested method if it returns a final status code.
2807    </t>
2808    <t> An origin server &SHOULD-NOT;  send a 100 (Continue) response if
2809        the request message does not include an Expect request-header
2810        field with the "100-continue" expectation, and &MUST-NOT; send a
2811        100 (Continue) response if such a request comes from an HTTP/1.0
2812        (or earlier) client. There is an exception to this rule: for
2813        compatibility with <xref target="RFC2068"/>, a server &MAY; send a 100 (Continue)
2814        status code in response to an HTTP/1.1 PUT or POST request that does
2815        not include an Expect request-header field with the "100-continue"
2816        expectation. This exception, the purpose of which is
2817        to minimize any client processing delays associated with an
2818        undeclared wait for 100 (Continue) status code, applies only to
2819        HTTP/1.1 requests, and not to requests with any other HTTP-version
2820        value.
2821    </t>
2822    <t> An origin server &MAY; omit a 100 (Continue) response if it has
2823        already received some or all of the request body for the
2824        corresponding request.
2825    </t>
2826    <t> An origin server that sends a 100 (Continue) response &MUST;
2827    ultimately send a final status code, once the request body is
2828        received and processed, unless it terminates the transport
2829        connection prematurely.
2830    </t>
2831    <t> If an origin server receives a request that does not include an
2832        Expect request-header field with the "100-continue" expectation,
2833        the request includes a request body, and the server responds
2834        with a final status code before reading the entire request body
2835        from the transport connection, then the server &SHOULD-NOT;  close
2836        the transport connection until it has read the entire request,
2837        or until the client closes the connection. Otherwise, the client
2838        might not reliably receive the response message. However, this
2839        requirement is not be construed as preventing a server from
2840        defending itself against denial-of-service attacks, or from
2841        badly broken client implementations.
2842      </t>
2843    </list>
2846   Requirements for HTTP/1.1 proxies:
2847  <list style="symbols">
2848    <t> If a proxy receives a request that includes an Expect request-header
2849        field with the "100-continue" expectation, and the proxy
2850        either knows that the next-hop server complies with HTTP/1.1 or
2851        higher, or does not know the HTTP version of the next-hop
2852        server, it &MUST; forward the request, including the Expect header
2853        field.
2854    </t>
2855    <t> If the proxy knows that the version of the next-hop server is
2856        HTTP/1.0 or lower, it &MUST-NOT; forward the request, and it &MUST;
2857        respond with a 417 (Expectation Failed) status code.
2858    </t>
2859    <t> Proxies &SHOULD; maintain a cache recording the HTTP version
2860        numbers received from recently-referenced next-hop servers.
2861    </t>
2862    <t> A proxy &MUST-NOT; forward a 100 (Continue) response if the
2863        request message was received from an HTTP/1.0 (or earlier)
2864        client and did not include an Expect request-header field with
2865        the "100-continue" expectation. This requirement overrides the
2866        general rule for forwarding of 1xx responses (see &status-1xx;).
2867    </t>
2868  </list>
2872<section title="Client Behavior if Server Prematurely Closes Connection" anchor="connection.premature">
2874   If an HTTP/1.1 client sends a request which includes a request body,
2875   but which does not include an Expect request-header field with the
2876   "100-continue" expectation, and if the client is not directly
2877   connected to an HTTP/1.1 origin server, and if the client sees the
2878   connection close before receiving a status line from the server, the
2879   client &SHOULD; retry the request.  If the client does retry this
2880   request, it &MAY; use the following "binary exponential backoff"
2881   algorithm to be assured of obtaining a reliable response:
2882  <list style="numbers">
2883    <t>
2884      Initiate a new connection to the server
2885    </t>
2886    <t>
2887      Transmit the request-header fields
2888    </t>
2889    <t>
2890      Initialize a variable R to the estimated round-trip time to the
2891         server (e.g., based on the time it took to establish the
2892         connection), or to a constant value of 5 seconds if the round-trip
2893         time is not available.
2894    </t>
2895    <t>
2896       Compute T = R * (2**N), where N is the number of previous
2897         retries of this request.
2898    </t>
2899    <t>
2900       Wait either for an error response from the server, or for T
2901         seconds (whichever comes first)
2902    </t>
2903    <t>
2904       If no error response is received, after T seconds transmit the
2905         body of the request.
2906    </t>
2907    <t>
2908       If client sees that the connection is closed prematurely,
2909         repeat from step 1 until the request is accepted, an error
2910         response is received, or the user becomes impatient and
2911         terminates the retry process.
2912    </t>
2913  </list>
2916   If at any point an error status code is received, the client
2917  <list style="symbols">
2918      <t>&SHOULD-NOT;  continue and</t>
2920      <t>&SHOULD; close the connection if it has not completed sending the
2921        request message.</t>
2922    </list>
2929<section title="Miscellaneous notes that might disappear" anchor="misc">
2930<section title="Scheme aliases considered harmful" anchor="scheme.aliases">
2932   <cref anchor="TBD-aliases-harmful">describe why aliases like webcal are harmful.</cref>
2936<section title="Use of HTTP for proxy communication" anchor="http.proxy">
2938   <cref anchor="TBD-proxy-other">Configured to use HTTP to proxy HTTP or other protocols.</cref>
2942<section title="Interception of HTTP for access control" anchor="http.intercept">
2944   <cref anchor="TBD-intercept">Interception of HTTP traffic for initiating access control.</cref>
2948<section title="Use of HTTP by other protocols" anchor="http.others">
2950   <cref anchor="TBD-profiles">Profiles of HTTP defined by other protocol.
2951   Extensions of HTTP like WebDAV.</cref>
2955<section title="Use of HTTP by media type specification" anchor="">
2957   <cref anchor="TBD-hypertext">Instructions on composing HTTP requests via hypertext formats.</cref>
2962<section title="Header Field Definitions" anchor="header.field.definitions">
2964   This section defines the syntax and semantics of HTTP/1.1 header fields
2965   related to message framing and transport protocols.
2968<section title="Connection" anchor="header.connection">
2969  <iref primary="true" item="Connection header field" x:for-anchor=""/>
2970  <iref primary="true" item="Header Fields" subitem="Connection" x:for-anchor=""/>
2971  <x:anchor-alias value="Connection"/>
2972  <x:anchor-alias value="connection-token"/>
2973  <x:anchor-alias value="Connection-v"/>
2975   The "Connection" general-header field allows the sender to specify
2976   options that are desired for that particular connection and &MUST-NOT;
2977   be communicated by proxies over further connections.
2980   The Connection header field's value has the following grammar:
2982<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Connection"/><iref primary="true" item="Grammar" subitem="Connection-v"/><iref primary="true" item="Grammar" subitem="connection-token"/>
2983  <x:ref>Connection</x:ref>       = "Connection" ":" <x:ref>OWS</x:ref> <x:ref>Connection-v</x:ref>
2984  <x:ref>Connection-v</x:ref>     = 1#<x:ref>connection-token</x:ref>
2985  <x:ref>connection-token</x:ref> = <x:ref>token</x:ref>
2988   HTTP/1.1 proxies &MUST; parse the Connection header field before a
2989   message is forwarded and, for each connection-token in this field,
2990   remove any header field(s) from the message with the same name as the
2991   connection-token. Connection options are signaled by the presence of
2992   a connection-token in the Connection header field, not by any
2993   corresponding additional header field(s), since the additional header
2994   field might not be sent if there are no parameters associated with that
2995   connection option.
2998   Message header fields listed in the Connection header field &MUST-NOT; include
2999   end-to-end header fields, such as Cache-Control.
3002   HTTP/1.1 defines the "close" connection option for the sender to
3003   signal that the connection will be closed after completion of the
3004   response. For example,
3006<figure><artwork type="example">
3007  Connection: close
3010   in either the request or the response header fields indicates that
3011   the connection &SHOULD-NOT;  be considered "persistent" (<xref target="persistent.connections"/>)
3012   after the current request/response is complete.
3015   An HTTP/1.1 client that does not support persistent connections &MUST;
3016   include the "close" connection option in every request message.
3019   An HTTP/1.1 server that does not support persistent connections &MUST;
3020   include the "close" connection option in every response message that
3021   does not have a 1xx (Informational) status code.
3024   A system receiving an HTTP/1.0 (or lower-version) message that
3025   includes a Connection header field &MUST;, for each connection-token in this
3026   field, remove and ignore any header field(s) from the message with
3027   the same name as the connection-token. This protects against mistaken
3028   forwarding of such header fields by pre-HTTP/1.1 proxies. See <xref target="compatibility.with.http.1.0.persistent.connections"/>.
3032<section title="Content-Length" anchor="header.content-length">
3033  <iref primary="true" item="Content-Length header field" x:for-anchor=""/>
3034  <iref primary="true" item="Header Fields" subitem="Content-Length" x:for-anchor=""/>
3035  <x:anchor-alias value="Content-Length"/>
3036  <x:anchor-alias value="Content-Length-v"/>
3038   The "Content-Length" header field indicates the size of the
3039   message-body, in decimal number of octets, for any message other than
3040   a response to the HEAD method or a response with a status code of 304.
3041   In the case of responses to the HEAD method, it indicates the size of
3042   the payload body (not including any potential transfer-coding) that
3043   would have been sent had the request been a GET.
3044   In the case of the 304 (Not Modified) response, it indicates the size of
3045   the payload body (not including any potential transfer-coding) that
3046   would have been sent in a 200 (OK) response.
3048<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Length"/><iref primary="true" item="Grammar" subitem="Content-Length-v"/>
3049  <x:ref>Content-Length</x:ref>   = "Content-Length" ":" <x:ref>OWS</x:ref> 1*<x:ref>Content-Length-v</x:ref>
3050  <x:ref>Content-Length-v</x:ref> = 1*<x:ref>DIGIT</x:ref>
3053   An example is
3055<figure><artwork type="example">
3056  Content-Length: 3495
3059   Implementations &SHOULD; use this field to indicate the message-body
3060   length when no transfer-coding is being applied and the
3061   payload's body length can be determined prior to being transferred.
3062   <xref target="message.body"/> describes how recipients determine the length
3063   of a message-body.
3066   Any Content-Length greater than or equal to zero is a valid value.
3069   Note that the use of this field in HTTP is significantly different from
3070   the corresponding definition in MIME, where it is an optional field
3071   used within the "message/external-body" content-type.
3075<section title="Date" anchor="">
3076  <iref primary="true" item="Date header field" x:for-anchor=""/>
3077  <iref primary="true" item="Header Fields" subitem="Date" x:for-anchor=""/>
3078  <x:anchor-alias value="Date"/>
3079  <x:anchor-alias value="Date-v"/>
3081   The "Date" general-header field represents the date and time at which
3082   the message was originated, having the same semantics as the Origination
3083   Date Field (orig-date) defined in <xref target="RFC5322" x:fmt="of" x:sec="3.6.1"/>.
3084   The field value is an HTTP-date, as described in <xref target=""/>;
3085   it &MUST; be sent in rfc1123-date format.
3087<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Date"/><iref primary="true" item="Grammar" subitem="Date-v"/>
3088  <x:ref>Date</x:ref>   = "Date" ":" <x:ref>OWS</x:ref> <x:ref>Date-v</x:ref>
3089  <x:ref>Date-v</x:ref> = <x:ref>HTTP-date</x:ref>
3092   An example is
3094<figure><artwork type="example">
3095  Date: Tue, 15 Nov 1994 08:12:31 GMT
3098   Origin servers &MUST; include a Date header field in all responses,
3099   except in these cases:
3100  <list style="numbers">
3101      <t>If the response status code is 100 (Continue) or 101 (Switching
3102         Protocols), the response &MAY; include a Date header field, at
3103         the server's option.</t>
3105      <t>If the response status code conveys a server error, e.g., 500
3106         (Internal Server Error) or 503 (Service Unavailable), and it is
3107         inconvenient or impossible to generate a valid Date.</t>
3109      <t>If the server does not have a clock that can provide a
3110         reasonable approximation of the current time, its responses
3111         &MUST-NOT; include a Date header field. In this case, the rules
3112         in <xref target="clockless.origin.server.operation"/> &MUST; be followed.</t>
3113  </list>
3116   A received message that does not have a Date header field &MUST; be
3117   assigned one by the recipient if the message will be cached by that
3118   recipient or gatewayed via a protocol which requires a Date.
3121   Clients can use the Date header field as well; in order to keep request
3122   messages small, they are advised not to include it when it doesn't convey
3123   any useful information (as it is usually the case for requests that do not
3124   contain a payload).
3127   The HTTP-date sent in a Date header field &SHOULD-NOT;  represent a date and
3128   time subsequent to the generation of the message. It &SHOULD; represent
3129   the best available approximation of the date and time of message
3130   generation, unless the implementation has no means of generating a
3131   reasonably accurate date and time. In theory, the date ought to
3132   represent the moment just before the payload is generated. In
3133   practice, the date can be generated at any time during the message
3134   origination without affecting its semantic value.
3137<section title="Clockless Origin Server Operation" anchor="clockless.origin.server.operation">
3139   Some origin server implementations might not have a clock available.
3140   An origin server without a clock &MUST-NOT; assign Expires or Last-Modified
3141   values to a response, unless these values were associated
3142   with the resource by a system or user with a reliable clock. It &MAY;
3143   assign an Expires value that is known, at or before server
3144   configuration time, to be in the past (this allows "pre-expiration"
3145   of responses without storing separate Expires values for each
3146   resource).
3151<section title="Host" anchor="">
3152  <iref primary="true" item="Host header field" x:for-anchor=""/>
3153  <iref primary="true" item="Header Fields" subitem="Host" x:for-anchor=""/>
3154  <x:anchor-alias value="Host"/>
3155  <x:anchor-alias value="Host-v"/>
3157   The "Host" request-header field specifies the Internet host and port
3158   number of the resource being requested, allowing the origin server or
3159   gateway to differentiate between internally-ambiguous URLs, such as the root
3160   "/" URL of a server for multiple host names on a single IP address.
3163   The Host field value &MUST; represent the naming authority of the origin
3164   server or gateway given by the original URL obtained from the user or
3165   referring resource (generally an http URI, as described in
3166   <xref target="http.uri"/>).
3168<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Host"/><iref primary="true" item="Grammar" subitem="Host-v"/>
3169  <x:ref>Host</x:ref>   = "Host" ":" <x:ref>OWS</x:ref> <x:ref>Host-v</x:ref>
3170  <x:ref>Host-v</x:ref> = <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ; <xref target="http.uri"/>
3173   A "host" without any trailing port information implies the default
3174   port for the service requested (e.g., "80" for an HTTP URL). For
3175   example, a request on the origin server for
3176   &lt;; would properly include:
3178<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
3179GET /pub/WWW/ HTTP/1.1
3183   A client &MUST; include a Host header field in all HTTP/1.1 request
3184   messages. If the requested URI does not include an Internet host
3185   name for the service being requested, then the Host header field &MUST;
3186   be given with an empty value. An HTTP/1.1 proxy &MUST; ensure that any
3187   request message it forwards does contain an appropriate Host header
3188   field that identifies the service being requested by the proxy. All
3189   Internet-based HTTP/1.1 servers &MUST; respond with a 400 (Bad Request)
3190   status code to any HTTP/1.1 request message which lacks a Host header
3191   field.
3194   See Sections <xref target="" format="counter"/>
3195   and <xref target="" format="counter"/>
3196   for other requirements relating to Host.
3200<section title="TE" anchor="header.te">
3201  <iref primary="true" item="TE header field" x:for-anchor=""/>
3202  <iref primary="true" item="Header Fields" subitem="TE" x:for-anchor=""/>
3203  <x:anchor-alias value="TE"/>
3204  <x:anchor-alias value="TE-v"/>
3205  <x:anchor-alias value="t-codings"/>
3206  <x:anchor-alias value="te-params"/>
3207  <x:anchor-alias value="te-ext"/>
3209   The "TE" request-header field indicates what extension transfer-codings
3210   it is willing to accept in the response, and whether or not it is
3211   willing to accept trailer fields in a chunked transfer-coding.
3214   Its value consists of the keyword "trailers" and/or a comma-separated
3215   list of extension transfer-coding names with optional accept
3216   parameters (as described in <xref target="transfer.codings"/>).
3218<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="TE"/><iref primary="true" item="Grammar" subitem="TE-v"/><iref primary="true" item="Grammar" subitem="t-codings"/><iref primary="true" item="Grammar" subitem="te-params"/><iref primary="true" item="Grammar" subitem="te-ext"/>
3219  <x:ref>TE</x:ref>        = "TE" ":" <x:ref>OWS</x:ref> <x:ref>TE-v</x:ref>
3220  <x:ref>TE-v</x:ref>      = #<x:ref>t-codings</x:ref>
3221  <x:ref>t-codings</x:ref> = "trailers" / ( <x:ref>transfer-extension</x:ref> [ <x:ref>te-params</x:ref> ] )
3222  <x:ref>te-params</x:ref> = <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref> *( <x:ref>te-ext</x:ref> )
3223  <x:ref>te-ext</x:ref>    = <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>token</x:ref> [ "=" <x:ref>word</x:ref> ]
3226   The presence of the keyword "trailers" indicates that the client is
3227   willing to accept trailer fields in a chunked transfer-coding, as
3228   defined in <xref target="chunked.encoding"/>. This keyword is reserved for use with
3229   transfer-coding values even though it does not itself represent a
3230   transfer-coding.
3233   Examples of its use are:
3235<figure><artwork type="example">
3236  TE: deflate
3237  TE:
3238  TE: trailers, deflate;q=0.5
3241   The TE header field only applies to the immediate connection.
3242   Therefore, the keyword &MUST; be supplied within a Connection header
3243   field (<xref target="header.connection"/>) whenever TE is present in an HTTP/1.1 message.
3246   A server tests whether a transfer-coding is acceptable, according to
3247   a TE field, using these rules:
3248  <list style="numbers">
3249    <x:lt>
3250      <t>The "chunked" transfer-coding is always acceptable. If the
3251         keyword "trailers" is listed, the client indicates that it is
3252         willing to accept trailer fields in the chunked response on
3253         behalf of itself and any downstream clients. The implication is
3254         that, if given, the client is stating that either all
3255         downstream clients are willing to accept trailer fields in the
3256         forwarded response, or that it will attempt to buffer the
3257         response on behalf of downstream recipients.
3258      </t><t>
3259         <x:h>Note:</x:h> HTTP/1.1 does not define any means to limit the size of a
3260         chunked response such that a client can be assured of buffering
3261         the entire response.</t>
3262    </x:lt>
3263    <x:lt>
3264      <t>If the transfer-coding being tested is one of the transfer-codings
3265         listed in the TE field, then it is acceptable unless it
3266         is accompanied by a qvalue of 0. (As defined in <xref target="quality.values"/>, a
3267         qvalue of 0 means "not acceptable".)</t>
3268    </x:lt>
3269    <x:lt>
3270      <t>If multiple transfer-codings are acceptable, then the
3271         acceptable transfer-coding with the highest non-zero qvalue is
3272         preferred.  The "chunked" transfer-coding always has a qvalue
3273         of 1.</t>
3274    </x:lt>
3275  </list>
3278   If the TE field-value is empty or if no TE field is present, the only
3279   transfer-coding is "chunked". A message with no transfer-coding is
3280   always acceptable.
3284<section title="Trailer" anchor="header.trailer">
3285  <iref primary="true" item="Trailer header field" x:for-anchor=""/>
3286  <iref primary="true" item="Header Fields" subitem="Trailer" x:for-anchor=""/>
3287  <x:anchor-alias value="Trailer"/>
3288  <x:anchor-alias value="Trailer-v"/>
3290   The "Trailer" general-header field indicates that the given set of
3291   header fields is present in the trailer of a message encoded with
3292   chunked transfer-coding.
3294<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Trailer"/><iref primary="true" item="Grammar" subitem="Trailer-v"/>
3295  <x:ref>Trailer</x:ref>   = "Trailer" ":" <x:ref>OWS</x:ref> <x:ref>Trailer-v</x:ref>
3296  <x:ref>Trailer-v</x:ref> = 1#<x:ref>field-name</x:ref>
3299   An HTTP/1.1 message &SHOULD; include a Trailer header field in a
3300   message using chunked transfer-coding with a non-empty trailer. Doing
3301   so allows the recipient to know which header fields to expect in the
3302   trailer.
3305   If no Trailer header field is present, the trailer &SHOULD-NOT;  include
3306   any header fields. See <xref target="chunked.encoding"/> for restrictions on the use of
3307   trailer fields in a "chunked" transfer-coding.
3310   Message header fields listed in the Trailer header field &MUST-NOT;
3311   include the following header fields:
3312  <list style="symbols">
3313    <t>Transfer-Encoding</t>
3314    <t>Content-Length</t>
3315    <t>Trailer</t>
3316  </list>
3320<section title="Transfer-Encoding" anchor="header.transfer-encoding">
3321  <iref primary="true" item="Transfer-Encoding header field" x:for-anchor=""/>
3322  <iref primary="true" item="Header Fields" subitem="Transfer-Encoding" x:for-anchor=""/>
3323  <x:anchor-alias value="Transfer-Encoding"/>
3324  <x:anchor-alias value="Transfer-Encoding-v"/>
3326   The "Transfer-Encoding" general-header field indicates what transfer-codings
3327   (if any) have been applied to the message body. It differs from
3328   Content-Encoding (&content-codings;) in that transfer-codings are a property
3329   of the message (and therefore are removed by intermediaries), whereas
3330   content-codings are not.
3332<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/><iref primary="true" item="Grammar" subitem="Transfer-Encoding-v"/>
3333  <x:ref>Transfer-Encoding</x:ref>   = "Transfer-Encoding" ":" <x:ref>OWS</x:ref>
3334                        <x:ref>Transfer-Encoding-v</x:ref>
3335  <x:ref>Transfer-Encoding-v</x:ref> = 1#<x:ref>transfer-coding</x:ref>
3338   Transfer-codings are defined in <xref target="transfer.codings"/>. An example is:
3340<figure><artwork type="example">
3341  Transfer-Encoding: chunked
3344   If multiple encodings have been applied to a representation, the transfer-codings
3345   &MUST; be listed in the order in which they were applied.
3346   Additional information about the encoding parameters &MAY; be provided
3347   by other header fields not defined by this specification.
3350   Many older HTTP/1.0 applications do not understand the Transfer-Encoding
3351   header field.
3355<section title="Upgrade" anchor="header.upgrade">
3356  <iref primary="true" item="Upgrade header field" x:for-anchor=""/>
3357  <iref primary="true" item="Header Fields" subitem="Upgrade" x:for-anchor=""/>
3358  <x:anchor-alias value="Upgrade"/>
3359  <x:anchor-alias value="Upgrade-v"/>
3361   The "Upgrade" general-header field allows the client to specify what
3362   additional communication protocols it would like to use, if the server
3363   chooses to switch protocols. Servers can use it to indicate what protocols
3364   they are willing to switch to.
3366<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Upgrade"/><iref primary="true" item="Grammar" subitem="Upgrade-v"/>
3367  <x:ref>Upgrade</x:ref>   = "Upgrade" ":" <x:ref>OWS</x:ref> <x:ref>Upgrade-v</x:ref>
3368  <x:ref>Upgrade-v</x:ref> = 1#<x:ref>product</x:ref>
3371   For example,
3373<figure><artwork type="example">
3374  Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
3377   The Upgrade header field is intended to provide a simple mechanism
3378   for transition from HTTP/1.1 to some other, incompatible protocol. It
3379   does so by allowing the client to advertise its desire to use another
3380   protocol, such as a later version of HTTP with a higher major version
3381   number, even though the current request has been made using HTTP/1.1.
3382   This eases the difficult transition between incompatible protocols by
3383   allowing the client to initiate a request in the more commonly
3384   supported protocol while indicating to the server that it would like
3385   to use a "better" protocol if available (where "better" is determined
3386   by the server, possibly according to the nature of the method and/or
3387   resource being requested).
3390   The Upgrade header field only applies to switching application-layer
3391   protocols upon the existing transport-layer connection. Upgrade
3392   cannot be used to insist on a protocol change; its acceptance and use
3393   by the server is optional. The capabilities and nature of the
3394   application-layer communication after the protocol change is entirely
3395   dependent upon the new protocol chosen, although the first action
3396   after changing the protocol &MUST; be a response to the initial HTTP
3397   request containing the Upgrade header field.
3400   The Upgrade header field only applies to the immediate connection.
3401   Therefore, the upgrade keyword &MUST; be supplied within a Connection
3402   header field (<xref target="header.connection"/>) whenever Upgrade is present in an
3403   HTTP/1.1 message.
3406   The Upgrade header field cannot be used to indicate a switch to a
3407   protocol on a different connection. For that purpose, it is more
3408   appropriate to use a 3xx redirection response (&status-3xx;).
3411   Servers &MUST; include the "Upgrade" header field in 101 (Switching
3412   Protocols) responses to indicate which protocol(s) are being switched to,
3413   and &MUST; include it in 426 (Upgrade Required) responses to indicate
3414   acceptable protocols to upgrade to. Servers &MAY; include it in any other
3415   response to indicate that they are willing to upgrade to one of the
3416   specified protocols.
3419   This specification only defines the protocol name "HTTP" for use by
3420   the family of Hypertext Transfer Protocols, as defined by the HTTP
3421   version rules of <xref target="http.version"/> and future updates to this
3422   specification. Additional tokens can be registered with IANA using the
3423   registration procedure defined below. 
3426<section title="Upgrade Token Registry" anchor="upgrade.token.registry">
3428   The HTTP Upgrade Token Registry defines the name space for product
3429   tokens used to identify protocols in the Upgrade header field.
3430   Each registered token is associated with contact information and
3431   an optional set of specifications that details how the connection
3432   will be processed after it has been upgraded.
3435   Registrations are allowed on a First Come First Served basis as
3436   described in <xref target="RFC5226" x:sec="4.1" x:fmt="of"/>. The
3437   specifications need not be IETF documents or be subject to IESG review.
3438   Registrations are subject to the following rules:
3439  <list style="numbers">
3440    <t>A token, once registered, stays registered forever.</t>
3441    <t>The registration &MUST; name a responsible party for the
3442       registration.</t>
3443    <t>The registration &MUST; name a point of contact.</t>
3444    <t>The registration &MAY; name a set of specifications associated with that
3445       token. Such specifications need not be publicly available.</t>
3446    <t>The responsible party &MAY; change the registration at any time.
3447       The IANA will keep a record of all such changes, and make them
3448       available upon request.</t>
3449    <t>The responsible party for the first registration of a "product"
3450       token &MUST; approve later registrations of a "version" token
3451       together with that "product" token before they can be registered.</t>
3452    <t>If absolutely required, the IESG &MAY; reassign the responsibility
3453       for a token. This will normally only be used in the case when a
3454       responsible party cannot be contacted.</t>
3455  </list>
3462<section title="Via" anchor="header.via">
3463  <iref primary="true" item="Via header field" x:for-anchor=""/>
3464  <iref primary="true" item="Header Fields" subitem="Via" x:for-anchor=""/>
3465  <x:anchor-alias value="protocol-name"/>
3466  <x:anchor-alias value="protocol-version"/>
3467  <x:anchor-alias value="pseudonym"/>
3468  <x:anchor-alias value="received-by"/>
3469  <x:anchor-alias value="received-protocol"/>
3470  <x:anchor-alias value="Via"/>
3471  <x:anchor-alias value="Via-v"/>
3473   The "Via" general-header field &MUST; be used by gateways and proxies to
3474   indicate the intermediate protocols and recipients between the user
3475   agent and the server on requests, and between the origin server and
3476   the client on responses. It is analogous to the "Received" field defined in
3477   <xref target="RFC5322" x:fmt="of" x:sec="3.6.7"/> and is intended to be used for tracking message forwards,
3478   avoiding request loops, and identifying the protocol capabilities of
3479   all senders along the request/response chain.
3481<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Via"/><iref primary="true" item="Grammar" subitem="Via-v"/><iref primary="true" item="Grammar" subitem="received-protocol"/><iref primary="true" item="Grammar" subitem="protocol-name"/><iref primary="true" item="Grammar" subitem="protocol-version"/><iref primary="true" item="Grammar" subitem="received-by"/><iref primary="true" item="Grammar" subitem="pseudonym"/>
3482  <x:ref>Via</x:ref>               = "Via" ":" <x:ref>OWS</x:ref> <x:ref>Via-v</x:ref>
3483  <x:ref>Via-v</x:ref>             = 1#( <x:ref>received-protocol</x:ref> <x:ref>RWS</x:ref> <x:ref>received-by</x:ref>
3484                          [ <x:ref>RWS</x:ref> <x:ref>comment</x:ref> ] )
3485  <x:ref>received-protocol</x:ref> = [ <x:ref>protocol-name</x:ref> "/" ] <x:ref>protocol-version</x:ref>
3486  <x:ref>protocol-name</x:ref>     = <x:ref>token</x:ref>
3487  <x:ref>protocol-version</x:ref>  = <x:ref>token</x:ref>
3488  <x:ref>received-by</x:ref>       = ( <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ) / <x:ref>pseudonym</x:ref>
3489  <x:ref>pseudonym</x:ref>         = <x:ref>token</x:ref>
3492   The received-protocol indicates the protocol version of the message
3493   received by the server or client along each segment of the
3494   request/response chain. The received-protocol version is appended to
3495   the Via field value when the message is forwarded so that information
3496   about the protocol capabilities of upstream applications remains
3497   visible to all recipients.
3500   The protocol-name is optional if and only if it would be "HTTP". The
3501   received-by field is normally the host and optional port number of a
3502   recipient server or client that subsequently forwarded the message.
3503   However, if the real host is considered to be sensitive information,
3504   it &MAY; be replaced by a pseudonym. If the port is not given, it &MAY;
3505   be assumed to be the default port of the received-protocol.
3508   Multiple Via field values represent each proxy or gateway that has
3509   forwarded the message. Each recipient &MUST; append its information
3510   such that the end result is ordered according to the sequence of
3511   forwarding applications.
3514   Comments &MAY; be used in the Via header field to identify the software
3515   of the recipient proxy or gateway, analogous to the User-Agent and
3516   Server header fields. However, all comments in the Via field are
3517   optional and &MAY; be removed by any recipient prior to forwarding the
3518   message.
3521   For example, a request message could be sent from an HTTP/1.0 user
3522   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
3523   forward the request to a public proxy at, which completes
3524   the request by forwarding it to the origin server at
3525   The request received by would then have the following
3526   Via header field:
3528<figure><artwork type="example">
3529  Via: 1.0 fred, 1.1 (Apache/1.1)
3532   Proxies and gateways used as a portal through a network firewall
3533   &SHOULD-NOT;, by default, forward the names and ports of hosts within
3534   the firewall region. This information &SHOULD; only be propagated if
3535   explicitly enabled. If not enabled, the received-by host of any host
3536   behind the firewall &SHOULD; be replaced by an appropriate pseudonym
3537   for that host.
3540   For organizations that have strong privacy requirements for hiding
3541   internal structures, a proxy &MAY; combine an ordered subsequence of
3542   Via header field entries with identical received-protocol values into
3543   a single such entry. For example,
3545<figure><artwork type="example">
3546  Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
3549  could be collapsed to
3551<figure><artwork type="example">
3552  Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
3555   Applications &SHOULD-NOT;  combine multiple entries unless they are all
3556   under the same organizational control and the hosts have already been
3557   replaced by pseudonyms. Applications &MUST-NOT; combine entries which
3558   have different received-protocol values.
3564<section title="IANA Considerations" anchor="IANA.considerations">
3566<section title="Header Field Registration" anchor="header.field.registration">
3568   The Message Header Field Registry located at <eref target=""/> shall be updated
3569   with the permanent registrations below (see <xref target="RFC3864"/>):
3571<?BEGININC p1-messaging.iana-headers ?>
3572<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
3573<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
3574   <ttcol>Header Field Name</ttcol>
3575   <ttcol>Protocol</ttcol>
3576   <ttcol>Status</ttcol>
3577   <ttcol>Reference</ttcol>
3579   <c>Connection</c>
3580   <c>http</c>
3581   <c>standard</c>
3582   <c>
3583      <xref target="header.connection"/>
3584   </c>
3585   <c>Content-Length</c>
3586   <c>http</c>
3587   <c>standard</c>
3588   <c>
3589      <xref target="header.content-length"/>
3590   </c>
3591   <c>Date</c>
3592   <c>http</c>
3593   <c>standard</c>
3594   <c>
3595      <xref target=""/>
3596   </c>
3597   <c>Host</c>
3598   <c>http</c>
3599   <c>standard</c>
3600   <c>
3601      <xref target=""/>
3602   </c>
3603   <c>TE</c>
3604   <c>http</c>
3605   <c>standard</c>
3606   <c>
3607      <xref target="header.te"/>
3608   </c>
3609   <c>Trailer</c>
3610   <c>http</c>
3611   <c>standard</c>
3612   <c>
3613      <xref target="header.trailer"/>
3614   </c>
3615   <c>Transfer-Encoding</c>
3616   <c>http</c>
3617   <c>standard</c>
3618   <c>
3619      <xref target="header.transfer-encoding"/>
3620   </c>
3621   <c>Upgrade</c>
3622   <c>http</c>
3623   <c>standard</c>
3624   <c>
3625      <xref target="header.upgrade"/>
3626   </c>
3627   <c>Via</c>
3628   <c>http</c>
3629   <c>standard</c>
3630   <c>
3631      <xref target="header.via"/>
3632   </c>
3635<?ENDINC p1-messaging.iana-headers ?>
3637   The change controller is: "IETF ( - Internet Engineering Task Force".
3641<section title="URI Scheme Registration" anchor="uri.scheme.registration">
3643   The entries for the "http" and "https" URI Schemes in the registry located at
3644   <eref target=""/>
3645   shall be updated to point to Sections <xref target="http.uri" format="counter"/>
3646   and <xref target="https.uri" format="counter"/> of this document
3647   (see <xref target="RFC4395"/>).
3651<section title="Internet Media Type Registrations" anchor="">
3653   This document serves as the specification for the Internet media types
3654   "message/http" and "application/http". The following is to be registered with
3655   IANA (see <xref target="RFC4288"/>).
3657<section title="Internet Media Type message/http" anchor="">
3658<iref item="Media Type" subitem="message/http" primary="true"/>
3659<iref item="message/http Media Type" primary="true"/>
3661   The message/http type can be used to enclose a single HTTP request or
3662   response message, provided that it obeys the MIME restrictions for all
3663   "message" types regarding line length and encodings.
3666  <list style="hanging" x:indent="12em">
3667    <t hangText="Type name:">
3668      message
3669    </t>
3670    <t hangText="Subtype name:">
3671      http
3672    </t>
3673    <t hangText="Required parameters:">
3674      none
3675    </t>
3676    <t hangText="Optional parameters:">
3677      version, msgtype
3678      <list style="hanging">
3679        <t hangText="version:">
3680          The HTTP-Version number of the enclosed message
3681          (e.g., "1.1"). If not present, the version can be
3682          determined from the first line of the body.
3683        </t>
3684        <t hangText="msgtype:">
3685          The message type &mdash; "request" or "response". If not
3686          present, the type can be determined from the first
3687          line of the body.
3688        </t>
3689      </list>
3690    </t>
3691    <t hangText="Encoding considerations:">
3692      only "7bit", "8bit", or "binary" are permitted
3693    </t>
3694    <t hangText="Security considerations:">
3695      none
3696    </t>
3697    <t hangText="Interoperability considerations:">
3698      none
3699    </t>
3700    <t hangText="Published specification:">
3701      This specification (see <xref target=""/>).
3702    </t>
3703    <t hangText="Applications that use this media type:">
3704    </t>
3705    <t hangText="Additional information:">
3706      <list style="hanging">
3707        <t hangText="Magic number(s):">none</t>
3708        <t hangText="File extension(s):">none</t>
3709        <t hangText="Macintosh file type code(s):">none</t>
3710      </list>
3711    </t>
3712    <t hangText="Person and email address to contact for further information:">
3713      See Authors Section.
3714    </t>
3715    <t hangText="Intended usage:">
3716      COMMON
3717    </t>
3718    <t hangText="Restrictions on usage:">
3719      none
3720    </t>
3721    <t hangText="Author/Change controller:">
3722      IESG
3723    </t>
3724  </list>
3727<section title="Internet Media Type application/http" anchor="">
3728<iref item="Media Type" subitem="application/http" primary="true"/>
3729<iref item="application/http Media Type" primary="true"/>
3731   The application/http type can be used to enclose a pipeline of one or more
3732   HTTP request or response messages (not intermixed).
3735  <list style="hanging" x:indent="12em">
3736    <t hangText="Type name:">
3737      application
3738    </t>
3739    <t hangText="Subtype name:">
3740      http
3741    </t>
3742    <t hangText="Required parameters:">
3743      none
3744    </t>
3745    <t hangText="Optional parameters:">
3746      version, msgtype
3747      <list style="hanging">
3748        <t hangText="version:">
3749          The HTTP-Version number of the enclosed messages
3750          (e.g., "1.1"). If not present, the version can be
3751          determined from the first line of the body.
3752        </t>
3753        <t hangText="msgtype:">
3754          The message type &mdash; "request" or "response". If not
3755          present, the type can be determined from the first
3756          line of the body.
3757        </t>
3758      </list>
3759    </t>
3760    <t hangText="Encoding considerations:">
3761      HTTP messages enclosed by this type
3762      are in "binary" format; use of an appropriate
3763      Content-Transfer-Encoding is required when
3764      transmitted via E-mail.
3765    </t>
3766    <t hangText="Security considerations:">
3767      none
3768    </t>
3769    <t hangText="Interoperability considerations:">
3770      none
3771    </t>
3772    <t hangText="Published specification:">
3773      This specification (see <xref target=""/>).
3774    </t>
3775    <t hangText="Applications that use this media type:">
3776    </t>
3777    <t hangText="Additional information:">
3778      <list style="hanging">
3779        <t hangText="Magic number(s):">none</t>
3780        <t hangText="File extension(s):">none</t>
3781        <t hangText="Macintosh file type code(s):">none</t>
3782      </list>
3783    </t>
3784    <t hangText="Person and email address to contact for further information:">
3785      See Authors Section.
3786    </t>
3787    <t hangText="Intended usage:">
3788      COMMON
3789    </t>
3790    <t hangText="Restrictions on usage:">
3791      none
3792    </t>
3793    <t hangText="Author/Change controller:">
3794      IESG
3795    </t>
3796  </list>
3801<section title="Transfer Coding Registry" anchor="transfer.coding.registration">
3803   The registration procedure for HTTP Transfer Codings is now defined by
3804   <xref target="transfer.coding.registry"/> of this document.
3807   The HTTP Transfer Codings Registry located at <eref target=""/>
3808   shall be updated with the registrations below:
3810<texttable align="left" suppress-title="true" anchor="iana.transfer.coding.registration.table">
3811   <ttcol>Name</ttcol>
3812   <ttcol>Description</ttcol>
3813   <ttcol>Reference</ttcol>
3814   <c>chunked</c>
3815   <c>Transfer in a series of chunks</c>
3816   <c>
3817      <xref target="chunked.encoding"/>
3818   </c>
3819   <c>compress</c>
3820   <c>UNIX "compress" program method</c>
3821   <c>
3822      <xref target="compress.coding"/>
3823   </c>
3824   <c>deflate</c>
3825   <c>"deflate" compression mechanism (<xref target="RFC1951"/>) used inside
3826   the "zlib" data format (<xref target="RFC1950"/>)
3827   </c>
3828   <c>
3829      <xref target="deflate.coding"/>
3830   </c>
3831   <c>gzip</c>
3832   <c>Same as GNU zip <xref target="RFC1952"/></c>
3833   <c>
3834      <xref target="gzip.coding"/>
3835   </c>
3839<section title="Upgrade Token Registration" anchor="upgrade.token.registration">
3841   The registration procedure for HTTP Upgrade Tokens &mdash; previously defined
3842   in <xref target="RFC2817" x:fmt="of" x:sec="7.2"/> &mdash; is now defined
3843   by <xref target="upgrade.token.registry"/> of this document.
3846   The HTTP Status Code Registry located at <eref target=""/>
3847   shall be updated with the registration below:
3849<texttable align="left" suppress-title="true">
3850   <ttcol>Value</ttcol>
3851   <ttcol>Description</ttcol>
3852   <ttcol>Reference</ttcol>
3854   <c>HTTP</c>
3855   <c>Hypertext Transfer Protocol</c>
3856   <c><xref target="http.version"/> of this specification</c>
3857<!-- IANA should add this without our instructions; emailed on June 05, 2009
3858   <c>TLS/1.0</c>
3859   <c>Transport Layer Security</c>
3860   <c><xref target="RFC2817"/></c> -->
3867<section title="Security Considerations" anchor="security.considerations">
3869   This section is meant to inform application developers, information
3870   providers, and users of the security limitations in HTTP/1.1 as
3871   described by this document. The discussion does not include
3872   definitive solutions to the problems revealed, though it does make
3873   some suggestions for reducing security risks.
3876<section title="Personal Information" anchor="personal.information">
3878   HTTP clients are often privy to large amounts of personal information
3879   (e.g., the user's name, location, mail address, passwords, encryption
3880   keys, etc.), and &SHOULD; be very careful to prevent unintentional
3881   leakage of this information.
3882   We very strongly recommend that a convenient interface be provided
3883   for the user to control dissemination of such information, and that
3884   designers and implementors be particularly careful in this area.
3885   History shows that errors in this area often create serious security
3886   and/or privacy problems and generate highly adverse publicity for the
3887   implementor's company.
3891<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
3893   A server is in the position to save personal data about a user's
3894   requests which might identify their reading patterns or subjects of
3895   interest. This information is clearly confidential in nature and its
3896   handling can be constrained by law in certain countries. People using
3897   HTTP to provide data are responsible for ensuring that
3898   such material is not distributed without the permission of any
3899   individuals that are identifiable by the published results.
3903<section title="Attacks Based On File and Path Names" anchor="attack.pathname">
3905   Implementations of HTTP origin servers &SHOULD; be careful to restrict
3906   the documents returned by HTTP requests to be only those that were
3907   intended by the server administrators. If an HTTP server translates
3908   HTTP URIs directly into file system calls, the server &MUST; take
3909   special care not to serve files that were not intended to be
3910   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
3911   other operating systems use ".." as a path component to indicate a
3912   directory level above the current one. On such a system, an HTTP
3913   server &MUST; disallow any such construct in the request-target if it
3914   would otherwise allow access to a resource outside those intended to
3915   be accessible via the HTTP server. Similarly, files intended for
3916   reference only internally to the server (such as access control
3917   files, configuration files, and script code) &MUST; be protected from
3918   inappropriate retrieval, since they might contain sensitive
3919   information. Experience has shown that minor bugs in such HTTP server
3920   implementations have turned into security risks.
3924<section title="DNS Spoofing" anchor="dns.spoofing">
3926   Clients using HTTP rely heavily on the Domain Name Service, and are
3927   thus generally prone to security attacks based on the deliberate
3928   mis-association of IP addresses and DNS names. Clients need to be
3929   cautious in assuming the continuing validity of an IP number/DNS name
3930   association.
3933   In particular, HTTP clients &SHOULD; rely on their name resolver for
3934   confirmation of an IP number/DNS name association, rather than
3935   caching the result of previous host name lookups. Many platforms
3936   already can cache host name lookups locally when appropriate, and
3937   they &SHOULD; be configured to do so. It is proper for these lookups to
3938   be cached, however, only when the TTL (Time To Live) information
3939   reported by the name server makes it likely that the cached
3940   information will remain useful.
3943   If HTTP clients cache the results of host name lookups in order to
3944   achieve a performance improvement, they &MUST; observe the TTL
3945   information reported by DNS.
3948   If HTTP clients do not observe this rule, they could be spoofed when
3949   a previously-accessed server's IP address changes. As network
3950   renumbering is expected to become increasingly common <xref target="RFC1900"/>, the
3951   possibility of this form of attack will grow. Observing this
3952   requirement thus reduces this potential security vulnerability.
3955   This requirement also improves the load-balancing behavior of clients
3956   for replicated servers using the same DNS name and reduces the
3957   likelihood of a user's experiencing failure in accessing sites which
3958   use that strategy.
3962<section title="Proxies and Caching" anchor="attack.proxies">
3964   By their very nature, HTTP proxies are men-in-the-middle, and
3965   represent an opportunity for man-in-the-middle attacks. Compromise of
3966   the systems on which the proxies run can result in serious security
3967   and privacy problems. Proxies have access to security-related
3968   information, personal information about individual users and
3969   organizations, and proprietary information belonging to users and
3970   content providers. A compromised proxy, or a proxy implemented or
3971   configured without regard to security and privacy considerations,
3972   might be used in the commission of a wide range of potential attacks.
3975   Proxy operators need to protect the systems on which proxies run as
3976   they would protect any system that contains or transports sensitive
3977   information. In particular, log information gathered at proxies often
3978   contains highly sensitive personal information, and/or information
3979   about organizations. Log information needs to be carefully guarded, and
3980   appropriate guidelines for use need to be developed and followed.
3981   (<xref target="abuse.of.server.log.information"/>).
3984   Proxy implementors need to consider the privacy and security
3985   implications of their design and coding decisions, and of the
3986   configuration options they provide to proxy operators (especially the
3987   default configuration).
3990   Users of a proxy need to be aware that proxies are no trustworthier than
3991   the people who run them; HTTP itself cannot solve this problem.
3994   The judicious use of cryptography, when appropriate, might suffice to
3995   protect against a broad range of security and privacy attacks. Such
3996   cryptography is beyond the scope of the HTTP/1.1 specification.
4000<section title="Denial of Service Attacks on Proxies" anchor="attack.DoS">
4002   They exist. They are hard to defend against. Research continues.
4003   Beware.
4008<section title="Acknowledgments" anchor="ack">
4010   HTTP has evolved considerably over the years. It has
4011   benefited from a large and active developer community &mdash; the many
4012   people who have participated on the www-talk mailing list &mdash; and it is
4013   that community which has been most responsible for the success of
4014   HTTP and of the World-Wide Web in general. Marc Andreessen, Robert
4015   Cailliau, Daniel W. Connolly, Bob Denny, John Franks, Jean-Francois
4016   Groff, Phillip M. Hallam-Baker, Hakon W. Lie, Ari Luotonen, Rob
4017   McCool, Lou Montulli, Dave Raggett, Tony Sanders, and Marc
4018   VanHeyningen deserve special recognition for their efforts in
4019   defining early aspects of the protocol.
4022   This document has benefited greatly from the comments of all those
4023   participating in the HTTP-WG. In addition to those already mentioned,
4024   the following individuals have contributed to this specification:
4027   Gary Adams, Harald Tveit Alvestrand, Keith Ball, Brian Behlendorf,
4028   Paul Burchard, Maurizio Codogno, Josh Cohen, Mike Cowlishaw, Roman Czyborra,
4029   Michael A. Dolan, Daniel DuBois, David J. Fiander, Alan Freier, Marc Hedlund, Greg Herlihy,
4030   Koen Holtman, Alex Hopmann, Bob Jernigan, Shel Kaphan, Rohit Khare,
4031   John Klensin, Martijn Koster, Alexei Kosut, David M. Kristol,
4032   Daniel LaLiberte, Ben Laurie, Paul J. Leach, Albert Lunde,
4033   John C. Mallery, Jean-Philippe Martin-Flatin, Mitra, David Morris,
4034   Gavin Nicol, Ross Patterson, Bill Perry, Jeffrey Perry, Scott Powers, Owen Rees,
4035   Luigi Rizzo, David Robinson, Marc Salomon, Rich Salz,
4036   Allan M. Schiffman, Jim Seidman, Chuck Shotton, Eric W. Sink,
4037   Simon E. Spero, Richard N. Taylor, Robert S. Thau,
4038   Bill (BearHeart) Weinman, Francois Yergeau, Mary Ellen Zurko.
4041   Thanks to the "cave men" of Palo Alto. You know who you are.
4044   Jim Gettys (the editor of <xref target="RFC2616"/>) wishes particularly
4045   to thank Roy Fielding, the editor of <xref target="RFC2068"/>, along
4046   with John Klensin, Jeff Mogul, Paul Leach, Dave Kristol, Koen
4047   Holtman, John Franks, Josh Cohen, Alex Hopmann, Scott Lawrence, and
4048   Larry Masinter for their help. And thanks go particularly to Jeff
4049   Mogul and Scott Lawrence for performing the "MUST/MAY/SHOULD" audit.
4052   The Apache Group, Anselm Baird-Smith, author of Jigsaw, and Henrik
4053   Frystyk implemented RFC 2068 early, and we wish to thank them for the
4054   discovery of many of the problems that this document attempts to
4055   rectify.
4058   This specification makes heavy use of the augmented BNF and generic
4059   constructs defined by David H. Crocker for <xref target="RFC5234"/>. Similarly, it
4060   reuses many of the definitions provided by Nathaniel Borenstein and
4061   Ned Freed for MIME <xref target="RFC2045"/>. We hope that their inclusion in this
4062   specification will help reduce past confusion over the relationship
4063   between HTTP and Internet mail message formats.
4067Acknowledgements TODO list
4069- Jeff Hodges ("effective request URI")
4077<references title="Normative References">
4079<reference anchor="ISO-8859-1">
4080  <front>
4081    <title>
4082     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
4083    </title>
4084    <author>
4085      <organization>International Organization for Standardization</organization>
4086    </author>
4087    <date year="1998"/>
4088  </front>
4089  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
4092<reference anchor="Part2">
4093  <front>
4094    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
4095    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4096      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4097      <address><email></email></address>
4098    </author>
4099    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4100      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4101      <address><email></email></address>
4102    </author>
4103    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4104      <organization abbrev="HP">Hewlett-Packard Company</organization>
4105      <address><email></email></address>
4106    </author>
4107    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4108      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4109      <address><email></email></address>
4110    </author>
4111    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4112      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4113      <address><email></email></address>
4114    </author>
4115    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4116      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4117      <address><email></email></address>
4118    </author>
4119    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4120      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4121      <address><email></email></address>
4122    </author>
4123    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4124      <organization abbrev="W3C">World Wide Web Consortium</organization>
4125      <address><email></email></address>
4126    </author>
4127    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4128      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4129      <address><email></email></address>
4130    </author>
4131    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4132  </front>
4133  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
4134  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
4137<reference anchor="Part3">
4138  <front>
4139    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
4140    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4141      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4142      <address><email></email></address>
4143    </author>
4144    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4145      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4146      <address><email></email></address>
4147    </author>
4148    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4149      <organization abbrev="HP">Hewlett-Packard Company</organization>
4150      <address><email></email></address>
4151    </author>
4152    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4153      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4154      <address><email></email></address>
4155    </author>
4156    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4157      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4158      <address><email></email></address>
4159    </author>
4160    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4161      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4162      <address><email></email></address>
4163    </author>
4164    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4165      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4166      <address><email></email></address>
4167    </author>
4168    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4169      <organization abbrev="W3C">World Wide Web Consortium</organization>
4170      <address><email></email></address>
4171    </author>
4172    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4173      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4174      <address><email></email></address>
4175    </author>
4176    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4177  </front>
4178  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
4179  <x:source href="p3-payload.xml" basename="p3-payload"/>
4182<reference anchor="Part6">
4183  <front>
4184    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
4185    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4186      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4187      <address><email></email></address>
4188    </author>
4189    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4190      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4191      <address><email></email></address>
4192    </author>
4193    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4194      <organization abbrev="HP">Hewlett-Packard Company</organization>
4195      <address><email></email></address>
4196    </author>
4197    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4198      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4199      <address><email></email></address>
4200    </author>
4201    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4202      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4203      <address><email></email></address>
4204    </author>
4205    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4206      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4207      <address><email></email></address>
4208    </author>
4209    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4210      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4211      <address><email></email></address>
4212    </author>
4213    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4214      <organization abbrev="W3C">World Wide Web Consortium</organization>
4215      <address><email></email></address>
4216    </author>
4217    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
4218      <address><email></email></address>
4219    </author>
4220    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4221      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4222      <address><email></email></address>
4223    </author>
4224    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4225  </front>
4226  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
4227  <x:source href="p6-cache.xml" basename="p6-cache"/>
4230<reference anchor="RFC5234">
4231  <front>
4232    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
4233    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
4234      <organization>Brandenburg InternetWorking</organization>
4235      <address>
4236        <email></email>
4237      </address> 
4238    </author>
4239    <author initials="P." surname="Overell" fullname="Paul Overell">
4240      <organization>THUS plc.</organization>
4241      <address>
4242        <email></email>
4243      </address>
4244    </author>
4245    <date month="January" year="2008"/>
4246  </front>
4247  <seriesInfo name="STD" value="68"/>
4248  <seriesInfo name="RFC" value="5234"/>
4251<reference anchor="RFC2119">
4252  <front>
4253    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
4254    <author initials="S." surname="Bradner" fullname="Scott Bradner">
4255      <organization>Harvard University</organization>
4256      <address><email></email></address>
4257    </author>
4258    <date month="March" year="1997"/>
4259  </front>
4260  <seriesInfo name="BCP" value="14"/>
4261  <seriesInfo name="RFC" value="2119"/>
4264<reference anchor="RFC3986">
4265 <front>
4266  <title abbrev='URI Generic Syntax'>Uniform Resource Identifier (URI): Generic Syntax</title>
4267  <author initials='T.' surname='Berners-Lee' fullname='Tim Berners-Lee'>
4268    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4269    <address>
4270       <email></email>
4271       <uri></uri>
4272    </address>
4273  </author>
4274  <author initials='R.' surname='Fielding' fullname='Roy T. Fielding'>
4275    <organization abbrev="Day Software">Day Software</organization>
4276    <address>
4277      <email></email>
4278      <uri></uri>
4279    </address>
4280  </author>
4281  <author initials='L.' surname='Masinter' fullname='Larry Masinter'>
4282    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
4283    <address>
4284      <email></email>
4285      <uri></uri>
4286    </address>
4287  </author>
4288  <date month='January' year='2005'></date>
4289 </front>
4290 <seriesInfo name="STD" value="66"/>
4291 <seriesInfo name="RFC" value="3986"/>
4294<reference anchor="USASCII">
4295  <front>
4296    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
4297    <author>
4298      <organization>American National Standards Institute</organization>
4299    </author>
4300    <date year="1986"/>
4301  </front>
4302  <seriesInfo name="ANSI" value="X3.4"/>
4305<reference anchor="RFC1950">
4306  <front>
4307    <title>ZLIB Compressed Data Format Specification version 3.3</title>
4308    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4309      <organization>Aladdin Enterprises</organization>
4310      <address><email></email></address>
4311    </author>
4312    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly"/>
4313    <date month="May" year="1996"/>
4314  </front>
4315  <seriesInfo name="RFC" value="1950"/>
4316  <annotation>
4317    RFC 1950 is an Informational RFC, thus it might be less stable than
4318    this specification. On the other hand, this downward reference was
4319    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4320    therefore it is unlikely to cause problems in practice. See also
4321    <xref target="BCP97"/>.
4322  </annotation>
4325<reference anchor="RFC1951">
4326  <front>
4327    <title>DEFLATE Compressed Data Format Specification version 1.3</title>
4328    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4329      <organization>Aladdin Enterprises</organization>
4330      <address><email></email></address>
4331    </author>
4332    <date month="May" year="1996"/>
4333  </front>
4334  <seriesInfo name="RFC" value="1951"/>
4335  <annotation>
4336    RFC 1951 is an Informational RFC, thus it might be less stable than
4337    this specification. On the other hand, this downward reference was
4338    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4339    therefore it is unlikely to cause problems in practice. See also
4340    <xref target="BCP97"/>.
4341  </annotation>
4344<reference anchor="RFC1952">
4345  <front>
4346    <title>GZIP file format specification version 4.3</title>
4347    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4348      <organization>Aladdin Enterprises</organization>
4349      <address><email></email></address>
4350    </author>
4351    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
4352      <address><email></email></address>
4353    </author>
4354    <author initials="M." surname="Adler" fullname="Mark Adler">
4355      <address><email></email></address>
4356    </author>
4357    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4358      <address><email></email></address>
4359    </author>
4360    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
4361      <address><email></email></address>
4362    </author>
4363    <date month="May" year="1996"/>
4364  </front>
4365  <seriesInfo name="RFC" value="1952"/>
4366  <annotation>
4367    RFC 1952 is an Informational RFC, thus it might be less stable than
4368    this specification. On the other hand, this downward reference was
4369    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4370    therefore it is unlikely to cause problems in practice. See also
4371    <xref target="BCP97"/>.
4372  </annotation>
4377<references title="Informative References">
4379<reference anchor="Nie1997" target="">
4380  <front>
4381    <title>Network Performance Effects of HTTP/1.1, CSS1, and PNG</title>
4382    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen"/>
4383    <author initials="J." surname="Gettys" fullname="J. Gettys"/>
4384    <author initials="E." surname="Prud'hommeaux" fullname="E. Prud'hommeaux"/>
4385    <author initials="H." surname="Lie" fullname="H. Lie"/>
4386    <author initials="C." surname="Lilley" fullname="C. Lilley"/>
4387    <date year="1997" month="September"/>
4388  </front>
4389  <seriesInfo name="ACM" value="Proceedings of the ACM SIGCOMM '97 conference on Applications, technologies, architectures, and protocols for computer communication SIGCOMM '97"/>
4392<reference anchor="Pad1995" target="">
4393  <front>
4394    <title>Improving HTTP Latency</title>
4395    <author initials="V.N." surname="Padmanabhan" fullname="Venkata N. Padmanabhan"/>
4396    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul"/>
4397    <date year="1995" month="December"/>
4398  </front>
4399  <seriesInfo name="Computer Networks and ISDN Systems" value="v. 28, pp. 25-35"/>
4402<reference anchor="RFC1123">
4403  <front>
4404    <title>Requirements for Internet Hosts - Application and Support</title>
4405    <author initials="R." surname="Braden" fullname="Robert Braden">
4406      <organization>University of Southern California (USC), Information Sciences Institute</organization>
4407      <address><email>Braden@ISI.EDU</email></address>
4408    </author>
4409    <date month="October" year="1989"/>
4410  </front>
4411  <seriesInfo name="STD" value="3"/>
4412  <seriesInfo name="RFC" value="1123"/>
4415<reference anchor="RFC1900">
4416  <front>
4417    <title>Renumbering Needs Work</title>
4418    <author initials="B." surname="Carpenter" fullname="Brian E. Carpenter">
4419      <organization>CERN, Computing and Networks Division</organization>
4420      <address><email></email></address>
4421    </author>
4422    <author initials="Y." surname="Rekhter" fullname="Yakov Rekhter">
4423      <organization>cisco Systems</organization>
4424      <address><email></email></address>
4425    </author>
4426    <date month="February" year="1996"/>
4427  </front>
4428  <seriesInfo name="RFC" value="1900"/>
4431<reference anchor='RFC1919'>
4432  <front>
4433    <title>Classical versus Transparent IP Proxies</title>
4434    <author initials='M.' surname='Chatel' fullname='Marc Chatel'>
4435      <address><email></email></address>
4436    </author>
4437    <date year='1996' month='March' />
4438  </front>
4439  <seriesInfo name='RFC' value='1919' />
4442<reference anchor="RFC1945">
4443  <front>
4444    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
4445    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4446      <organization>MIT, Laboratory for Computer Science</organization>
4447      <address><email></email></address>
4448    </author>
4449    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4450      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4451      <address><email></email></address>
4452    </author>
4453    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4454      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
4455      <address><email></email></address>
4456    </author>
4457    <date month="May" year="1996"/>
4458  </front>
4459  <seriesInfo name="RFC" value="1945"/>
4462<reference anchor="RFC2045">
4463  <front>
4464    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
4465    <author initials="N." surname="Freed" fullname="Ned Freed">
4466      <organization>Innosoft International, Inc.</organization>
4467      <address><email></email></address>
4468    </author>
4469    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
4470      <organization>First Virtual Holdings</organization>
4471      <address><email></email></address>
4472    </author>
4473    <date month="November" year="1996"/>
4474  </front>
4475  <seriesInfo name="RFC" value="2045"/>
4478<reference anchor="RFC2047">
4479  <front>
4480    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
4481    <author initials="K." surname="Moore" fullname="Keith Moore">
4482      <organization>University of Tennessee</organization>
4483      <address><email></email></address>
4484    </author>
4485    <date month="November" year="1996"/>
4486  </front>
4487  <seriesInfo name="RFC" value="2047"/>
4490<reference anchor="RFC2068">
4491  <front>
4492    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
4493    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
4494      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4495      <address><email></email></address>
4496    </author>
4497    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4498      <organization>MIT Laboratory for Computer Science</organization>
4499      <address><email></email></address>
4500    </author>
4501    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4502      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
4503      <address><email></email></address>
4504    </author>
4505    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4506      <organization>MIT Laboratory for Computer Science</organization>
4507      <address><email></email></address>
4508    </author>
4509    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4510      <organization>MIT Laboratory for Computer Science</organization>
4511      <address><email></email></address>
4512    </author>
4513    <date month="January" year="1997"/>
4514  </front>
4515  <seriesInfo name="RFC" value="2068"/>
4518<reference anchor="RFC2145">
4519  <front>
4520    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
4521    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
4522      <organization>Western Research Laboratory</organization>
4523      <address><email></email></address>
4524    </author>
4525    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4526      <organization>Department of Information and Computer Science</organization>
4527      <address><email></email></address>
4528    </author>
4529    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4530      <organization>MIT Laboratory for Computer Science</organization>
4531      <address><email></email></address>
4532    </author>
4533    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4534      <organization>W3 Consortium</organization>
4535      <address><email></email></address>
4536    </author>
4537    <date month="May" year="1997"/>
4538  </front>
4539  <seriesInfo name="RFC" value="2145"/>
4542<reference anchor="RFC2616">
4543  <front>
4544    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
4545    <author initials="R." surname="Fielding" fullname="R. Fielding">
4546      <organization>University of California, Irvine</organization>
4547      <address><email></email></address>
4548    </author>
4549    <author initials="J." surname="Gettys" fullname="J. Gettys">
4550      <organization>W3C</organization>
4551      <address><email></email></address>
4552    </author>
4553    <author initials="J." surname="Mogul" fullname="J. Mogul">
4554      <organization>Compaq Computer Corporation</organization>
4555      <address><email></email></address>
4556    </author>
4557    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
4558      <organization>MIT Laboratory for Computer Science</organization>
4559      <address><email></email></address>
4560    </author>
4561    <author initials="L." surname="Masinter" fullname="L. Masinter">
4562      <organization>Xerox Corporation</organization>
4563      <address><email></email></address>
4564    </author>
4565    <author initials="P." surname="Leach" fullname="P. Leach">
4566      <organization>Microsoft Corporation</organization>
4567      <address><email></email></address>
4568    </author>
4569    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
4570      <organization>W3C</organization>
4571      <address><email></email></address>
4572    </author>
4573    <date month="June" year="1999"/>
4574  </front>
4575  <seriesInfo name="RFC" value="2616"/>
4578<reference anchor='RFC2817'>
4579  <front>
4580    <title>Upgrading to TLS Within HTTP/1.1</title>
4581    <author initials='R.' surname='Khare' fullname='R. Khare'>
4582      <organization>4K Associates / UC Irvine</organization>
4583      <address><email></email></address>
4584    </author>
4585    <author initials='S.' surname='Lawrence' fullname='S. Lawrence'>
4586      <organization>Agranat Systems, Inc.</organization>
4587      <address><email></email></address>
4588    </author>
4589    <date year='2000' month='May' />
4590  </front>
4591  <seriesInfo name='RFC' value='2817' />
4594<reference anchor='RFC2818'>
4595  <front>
4596    <title>HTTP Over TLS</title>
4597    <author initials='E.' surname='Rescorla' fullname='Eric Rescorla'>
4598      <organization>RTFM, Inc.</organization>
4599      <address><email></email></address>
4600    </author>
4601    <date year='2000' month='May' />
4602  </front>
4603  <seriesInfo name='RFC' value='2818' />
4606<reference anchor='RFC2965'>
4607  <front>
4608    <title>HTTP State Management Mechanism</title>
4609    <author initials='D. M.' surname='Kristol' fullname='David M. Kristol'>
4610      <organization>Bell Laboratories, Lucent Technologies</organization>
4611      <address><email></email></address>
4612    </author>
4613    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
4614      <organization>, Inc.</organization>
4615      <address><email></email></address>
4616    </author>
4617    <date year='2000' month='October' />
4618  </front>
4619  <seriesInfo name='RFC' value='2965' />
4622<reference anchor='RFC3040'>
4623  <front>
4624    <title>Internet Web Replication and Caching Taxonomy</title>
4625    <author initials='I.' surname='Cooper' fullname='I. Cooper'>
4626      <organization>Equinix, Inc.</organization>
4627    </author>
4628    <author initials='I.' surname='Melve' fullname='I. Melve'>
4629      <organization>UNINETT</organization>
4630    </author>
4631    <author initials='G.' surname='Tomlinson' fullname='G. Tomlinson'>
4632      <organization>CacheFlow Inc.</organization>
4633    </author>
4634    <date year='2001' month='January' />
4635  </front>
4636  <seriesInfo name='RFC' value='3040' />
4639<reference anchor='RFC3864'>
4640  <front>
4641    <title>Registration Procedures for Message Header Fields</title>
4642    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
4643      <organization>Nine by Nine</organization>
4644      <address><email></email></address>
4645    </author>
4646    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
4647      <organization>BEA Systems</organization>
4648      <address><email></email></address>
4649    </author>
4650    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
4651      <organization>HP Labs</organization>
4652      <address><email></email></address>
4653    </author>
4654    <date year='2004' month='September' />
4655  </front>
4656  <seriesInfo name='BCP' value='90' />
4657  <seriesInfo name='RFC' value='3864' />
4660<reference anchor="RFC4288">
4661  <front>
4662    <title>Media Type Specifications and Registration Procedures</title>
4663    <author initials="N." surname="Freed" fullname="N. Freed">
4664      <organization>Sun Microsystems</organization>
4665      <address>
4666        <email></email>
4667      </address>
4668    </author>
4669    <author initials="J." surname="Klensin" fullname="J. Klensin">
4670      <address>
4671        <email></email>
4672      </address>
4673    </author>
4674    <date year="2005" month="December"/>
4675  </front>
4676  <seriesInfo name="BCP" value="13"/>
4677  <seriesInfo name="RFC" value="4288"/>
4680<reference anchor='RFC4395'>
4681  <front>
4682    <title>Guidelines and Registration Procedures for New URI Schemes</title>
4683    <author initials='T.' surname='Hansen' fullname='T. Hansen'>
4684      <organization>AT&amp;T Laboratories</organization>
4685      <address>
4686        <email></email>
4687      </address>
4688    </author>
4689    <author initials='T.' surname='Hardie' fullname='T. Hardie'>
4690      <organization>Qualcomm, Inc.</organization>
4691      <address>
4692        <email></email>
4693      </address>
4694    </author>
4695    <author initials='L.' surname='Masinter' fullname='L. Masinter'>
4696      <organization>Adobe Systems</organization>
4697      <address>
4698        <email></email>
4699      </address>
4700    </author>
4701    <date year='2006' month='February' />
4702  </front>
4703  <seriesInfo name='BCP' value='115' />
4704  <seriesInfo name='RFC' value='4395' />
4707<reference anchor='RFC5226'>
4708  <front>
4709    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
4710    <author initials='T.' surname='Narten' fullname='T. Narten'>
4711      <organization>IBM</organization>
4712      <address><email></email></address>
4713    </author>
4714    <author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'>
4715      <organization>Google</organization>
4716      <address><email></email></address>
4717    </author>
4718    <date year='2008' month='May' />
4719  </front>
4720  <seriesInfo name='BCP' value='26' />
4721  <seriesInfo name='RFC' value='5226' />
4724<reference anchor="RFC5322">
4725  <front>
4726    <title>Internet Message Format</title>
4727    <author initials="P." surname="Resnick" fullname="P. Resnick">
4728      <organization>Qualcomm Incorporated</organization>
4729    </author>
4730    <date year="2008" month="October"/>
4731  </front>
4732  <seriesInfo name="RFC" value="5322"/>
4735<reference anchor='draft-ietf-httpstate-cookie'>
4736  <front>
4737    <title>HTTP State Management Mechanism</title>
4738    <author initials="A." surname="Barth" fullname="Adam Barth">
4739      <organization abbrev="U.C. Berkeley">
4740        University of California, Berkeley
4741      </organization>
4742      <address><email></email></address>
4743    </author>
4744    <date year='2011' month='March' />
4745  </front>
4746  <seriesInfo name="Internet-Draft" value="draft-ietf-httpstate-cookie-23"/>
4749<reference anchor='BCP97'>
4750  <front>
4751    <title>Handling Normative References to Standards-Track Documents</title>
4752    <author initials='J.' surname='Klensin' fullname='J. Klensin'>
4753      <address>
4754        <email></email>
4755      </address>
4756    </author>
4757    <author initials='S.' surname='Hartman' fullname='S. Hartman'>
4758      <organization>MIT</organization>
4759      <address>
4760        <email></email>
4761      </address>
4762    </author>
4763    <date year='2007' month='June' />
4764  </front>
4765  <seriesInfo name='BCP' value='97' />
4766  <seriesInfo name='RFC' value='4897' />
4769<reference anchor="Kri2001" target="">
4770  <front>
4771    <title>HTTP Cookies: Standards, Privacy, and Politics</title>
4772    <author initials="D." surname="Kristol" fullname="David M. Kristol"/>
4773    <date year="2001" month="November"/>
4774  </front>
4775  <seriesInfo name="ACM Transactions on Internet Technology" value="Vol. 1, #2"/>
4778<reference anchor="Spe" target="">
4779  <front>
4780    <title>Analysis of HTTP Performance Problems</title>
4781    <author initials="S." surname="Spero" fullname="Simon E. Spero"/>
4782    <date/>
4783  </front>
4786<reference anchor="Tou1998" target="">
4787  <front>
4788  <title>Analysis of HTTP Performance</title>
4789  <author initials="J." surname="Touch" fullname="Joe Touch">
4790    <organization>USC/Information Sciences Institute</organization>
4791    <address><email></email></address>
4792  </author>
4793  <author initials="J." surname="Heidemann" fullname="John Heidemann">
4794    <organization>USC/Information Sciences Institute</organization>
4795    <address><email></email></address>
4796  </author>
4797  <author initials="K." surname="Obraczka" fullname="Katia Obraczka">
4798    <organization>USC/Information Sciences Institute</organization>
4799    <address><email></email></address>
4800  </author>
4801  <date year="1998" month="Aug"/>
4802  </front>
4803  <seriesInfo name="ISI Research Report" value="ISI/RR-98-463"/>
4804  <annotation>(original report dated Aug. 1996)</annotation>
4810<section title="Tolerant Applications" anchor="tolerant.applications">
4812   Although this document specifies the requirements for the generation
4813   of HTTP/1.1 messages, not all applications will be correct in their
4814   implementation. We therefore recommend that operational applications
4815   be tolerant of deviations whenever those deviations can be
4816   interpreted unambiguously.
4819   Clients &SHOULD; be tolerant in parsing the Status-Line and servers
4820   &SHOULD; be tolerant when parsing the Request-Line. In particular, they
4821   &SHOULD; accept any amount of WSP characters between fields, even though
4822   only a single SP is required.
4825   The line terminator for header fields is the sequence CRLF.
4826   However, we recommend that applications, when parsing such headers fields,
4827   recognize a single LF as a line terminator and ignore the leading CR.
4830   The character set of a representation &SHOULD; be labeled as the lowest
4831   common denominator of the character codes used within that representation, with
4832   the exception that not labeling the representation is preferred over labeling
4833   the representation with the labels US-ASCII or ISO-8859-1. See &payload;.
4836   Additional rules for requirements on parsing and encoding of dates
4837   and other potential problems with date encodings include:
4840  <list style="symbols">
4841     <t>HTTP/1.1 clients and caches &SHOULD; assume that an RFC-850 date
4842        which appears to be more than 50 years in the future is in fact
4843        in the past (this helps solve the "year 2000" problem).</t>
4845     <t>Although all date formats are specified to be case-sensitive,
4846        recipients &SHOULD; match day, week and timezone names
4847        case-insensitively.</t>
4849     <t>An HTTP/1.1 implementation &MAY; internally represent a parsed
4850        Expires date as earlier than the proper value, but &MUST-NOT;
4851        internally represent a parsed Expires date as later than the
4852        proper value.</t>
4854     <t>All expiration-related calculations &MUST; be done in GMT. The
4855        local time zone &MUST-NOT; influence the calculation or comparison
4856        of an age or expiration time.</t>
4858     <t>If an HTTP header field incorrectly carries a date value with a time
4859        zone other than GMT, it &MUST; be converted into GMT using the
4860        most conservative possible conversion.</t>
4861  </list>
4865<section title="Compatibility with Previous Versions" anchor="compatibility">
4867   HTTP has been in use by the World-Wide Web global information initiative
4868   since 1990. The first version of HTTP, later referred to as HTTP/0.9,
4869   was a simple protocol for hypertext data transfer across the Internet
4870   with only a single method and no metadata.
4871   HTTP/1.0, as defined by <xref target="RFC1945"/>, added a range of request
4872   methods and MIME-like messaging that could include metadata about the data
4873   transferred and modifiers on the request/response semantics. However,
4874   HTTP/1.0 did not sufficiently take into consideration the effects of
4875   hierarchical proxies, caching, the need for persistent connections, or
4876   name-based virtual hosts. The proliferation of incompletely-implemented
4877   applications calling themselves "HTTP/1.0" further necessitated a
4878   protocol version change in order for two communicating applications
4879   to determine each other's true capabilities.
4882   HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
4883   requirements that enable reliable implementations, adding only
4884   those new features that will either be safely ignored by an HTTP/1.0
4885   recipient or only sent when communicating with a party advertising
4886   compliance with HTTP/1.1.
4889   It is beyond the scope of a protocol specification to mandate
4890   compliance with previous versions. HTTP/1.1 was deliberately
4891   designed, however, to make supporting previous versions easy. It is
4892   worth noting that, at the time of composing this specification, we would
4893   expect general-purpose HTTP/1.1 servers to:
4894  <list style="symbols">
4895     <t>understand any valid request in the format of HTTP/1.0 and
4896        1.1;</t>
4898     <t>respond appropriately with a message in the same major version
4899        used by the client.</t>
4900  </list>
4903   And we would expect HTTP/1.1 clients to:
4904  <list style="symbols">
4905     <t>understand any valid response in the format of HTTP/1.0 or
4906        1.1.</t>
4907  </list>
4910   For most implementations of HTTP/1.0, each connection is established
4911   by the client prior to the request and closed by the server after
4912   sending the response. Some implementations implement the Keep-Alive
4913   version of persistent connections described in <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>.
4916<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
4918   This section summarizes major differences between versions HTTP/1.0
4919   and HTTP/1.1.
4922<section title="Changes to Simplify Multi-homed Web Servers and Conserve IP Addresses" anchor="">
4924   The requirements that clients and servers support the Host request-header
4925   field (<xref target=""/>), report an error if it is
4926   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-target"/>)
4927   are among the most important changes defined by this
4928   specification.
4931   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
4932   addresses and servers; there was no other established mechanism for
4933   distinguishing the intended server of a request than the IP address
4934   to which that request was directed. The changes outlined above will
4935   allow the Internet, once older HTTP clients are no longer common, to
4936   support multiple Web sites from a single IP address, greatly
4937   simplifying large operational Web servers, where allocation of many
4938   IP addresses to a single host has created serious problems. The
4939   Internet will also be able to recover the IP addresses that have been
4940   allocated for the sole purpose of allowing special-purpose domain
4941   names to be used in root-level HTTP URLs. Given the rate of growth of
4942   the Web, and the number of servers already deployed, it is extremely
4943   important that all implementations of HTTP (including updates to
4944   existing HTTP/1.0 applications) correctly implement these
4945   requirements:
4946  <list style="symbols">
4947     <t>Both clients and servers &MUST; support the Host request-header field.</t>
4949     <t>A client that sends an HTTP/1.1 request &MUST; send a Host header field.</t>
4951     <t>Servers &MUST; report a 400 (Bad Request) error if an HTTP/1.1
4952        request does not include a Host request-header field.</t>
4954     <t>Servers &MUST; accept absolute URIs.</t>
4955  </list>
4960<section title="Compatibility with HTTP/1.0 Persistent Connections" anchor="compatibility.with.http.1.0.persistent.connections">
4962   Some clients and servers might wish to be compatible with some
4963   previous implementations of persistent connections in HTTP/1.0
4964   clients and servers. Persistent connections in HTTP/1.0 are
4965   explicitly negotiated as they are not the default behavior. HTTP/1.0
4966   experimental implementations of persistent connections are faulty,
4967   and the new facilities in HTTP/1.1 are designed to rectify these
4968   problems. The problem was that some existing HTTP/1.0 clients might
4969   send Keep-Alive to a proxy server that doesn't understand
4970   Connection, which would then erroneously forward it to the next
4971   inbound server, which would establish the Keep-Alive connection and
4972   result in a hung HTTP/1.0 proxy waiting for the close on the
4973   response. The result is that HTTP/1.0 clients must be prevented from
4974   using Keep-Alive when talking to proxies.
4977   However, talking to proxies is the most important use of persistent
4978   connections, so that prohibition is clearly unacceptable. Therefore,
4979   we need some other mechanism for indicating a persistent connection
4980   is desired, which is safe to use even when talking to an old proxy
4981   that ignores Connection. Persistent connections are the default for
4982   HTTP/1.1 messages; we introduce a new keyword (Connection: close) for
4983   declaring non-persistence. See <xref target="header.connection"/>.
4986   The original HTTP/1.0 form of persistent connections (the Connection:
4987   Keep-Alive and Keep-Alive header field) is documented in <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>.
4991<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
4993  Empty list elements in list productions have been deprecated.
4994  (<xref target="notation.abnf"/>)
4997  Rules about implicit linear whitespace between certain grammar productions
4998  have been removed; now it's only allowed when specifically pointed out
4999  in the ABNF. The NUL character is no longer allowed in comment and quoted-string
5000  text. The quoted-pair rule no longer allows escaping control characters other than HTAB.
5001  Non-ASCII content in header fields and reason phrase has been obsoleted and
5002  made opaque (the TEXT rule was removed)
5003  (<xref target="basic.rules"/>)
5006  Clarify that HTTP-Version is case sensitive.
5007  (<xref target="http.version"/>)
5010  Require that invalid whitespace around field-names be rejected.
5011  (<xref target="header.fields"/>)
5014  Require recipients to handle bogus Content-Length header fields as errors.
5015  (<xref target="message.body"/>)
5018  Remove reference to non-existent identity transfer-coding value tokens.
5019  (Sections <xref format="counter" target="message.body"/> and
5020  <xref format="counter" target="transfer.codings"/>)
5023  Update use of abs_path production from RFC 1808 to the path-absolute + query
5024  components of RFC 3986. State that the asterisk form is allowed for the OPTIONS
5025  method only.
5026  (<xref target="request-target"/>)
5029  Clarification that the chunk length does not include the count of the octets
5030  in the chunk header and trailer. Furthermore disallowed line folding
5031  in chunk extensions.
5032  (<xref target="chunked.encoding"/>)
5035  Remove hard limit of two connections per server.
5036  (<xref target="persistent.practical"/>)
5039  Clarify exactly when close connection options must be sent.
5040  (<xref target="header.connection"/>)
5043  Define the semantics of the "Upgrade" header field in responses other than
5044  101 (this was incorporated from <xref target="RFC2817"/>).
5045  (<xref target="header.upgrade"/>)
5050<?BEGININC p1-messaging.abnf-appendix ?>
5051<section xmlns:x="" title="Collected ABNF" anchor="collected.abnf">
5053<artwork type="abnf" name="p1-messaging.parsed-abnf">
5054<x:ref>BWS</x:ref> = OWS
5056<x:ref>Cache-Control</x:ref> = &lt;Cache-Control, defined in [Part6], Section 3.4&gt;
5057<x:ref>Chunked-Body</x:ref> = *chunk last-chunk trailer-part CRLF
5058<x:ref>Connection</x:ref> = "Connection:" OWS Connection-v
5059<x:ref>Connection-v</x:ref> = *( "," OWS ) connection-token *( OWS "," [ OWS
5060 connection-token ] )
5061<x:ref>Content-Length</x:ref> = "Content-Length:" OWS 1*Content-Length-v
5062<x:ref>Content-Length-v</x:ref> = 1*DIGIT
5064<x:ref>Date</x:ref> = "Date:" OWS Date-v
5065<x:ref>Date-v</x:ref> = HTTP-date
5067<x:ref>GMT</x:ref> = %x47.4D.54 ; GMT
5069<x:ref>HTTP-Prot-Name</x:ref> = %x48.54.54.50 ; HTTP
5070<x:ref>HTTP-Version</x:ref> = HTTP-Prot-Name "/" 1*DIGIT "." 1*DIGIT
5071<x:ref>HTTP-date</x:ref> = rfc1123-date / obs-date
5072<x:ref>HTTP-message</x:ref> = start-line *( header-field CRLF ) CRLF [ message-body
5073 ]
5074<x:ref>Host</x:ref> = "Host:" OWS Host-v
5075<x:ref>Host-v</x:ref> = uri-host [ ":" port ]
5077<x:ref>MIME-Version</x:ref> = &lt;MIME-Version, defined in [Part3], Appendix A.1&gt;
5078<x:ref>Method</x:ref> = token
5080<x:ref>OWS</x:ref> = *( [ obs-fold ] WSP )
5082<x:ref>Pragma</x:ref> = &lt;Pragma, defined in [Part6], Section 3.4&gt;
5084<x:ref>RWS</x:ref> = 1*( [ obs-fold ] WSP )
5085<x:ref>Reason-Phrase</x:ref> = *( WSP / VCHAR / obs-text )
5086<x:ref>Request</x:ref> = Request-Line *( header-field CRLF ) CRLF [ message-body ]
5087<x:ref>Request-Line</x:ref> = Method SP request-target SP HTTP-Version CRLF
5088<x:ref>Response</x:ref> = Status-Line *( header-field CRLF ) CRLF [ message-body ]
5090<x:ref>Status-Code</x:ref> = 3DIGIT
5091<x:ref>Status-Line</x:ref> = HTTP-Version SP Status-Code SP Reason-Phrase CRLF
5093<x:ref>TE</x:ref> = "TE:" OWS TE-v
5094<x:ref>TE-v</x:ref> = [ ( "," / t-codings ) *( OWS "," [ OWS t-codings ] ) ]
5095<x:ref>Trailer</x:ref> = "Trailer:" OWS Trailer-v
5096<x:ref>Trailer-v</x:ref> = *( "," OWS ) field-name *( OWS "," [ OWS field-name ] )
5097<x:ref>Transfer-Encoding</x:ref> = "Transfer-Encoding:" OWS Transfer-Encoding-v
5098<x:ref>Transfer-Encoding-v</x:ref> = *( "," OWS ) transfer-coding *( OWS "," [ OWS
5099 transfer-coding ] )
5101<x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in [RFC3986], Section 4.1&gt;
5102<x:ref>Upgrade</x:ref> = "Upgrade:" OWS Upgrade-v
5103<x:ref>Upgrade-v</x:ref> = *( "," OWS ) product *( OWS "," [ OWS product ] )
5105<x:ref>Via</x:ref> = "Via:" OWS Via-v
5106<x:ref>Via-v</x:ref> = *( "," OWS ) received-protocol RWS received-by [ RWS comment
5107 ] *( OWS "," [ OWS received-protocol RWS received-by [ RWS comment ]
5108 ] )
5110<x:ref>Warning</x:ref> = &lt;Warning, defined in [Part6], Section 3.6&gt;
5112<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [RFC3986], Section 4.3&gt;
5113<x:ref>asctime-date</x:ref> = day-name SP date3 SP time-of-day SP year
5114<x:ref>attribute</x:ref> = token
5115<x:ref>authority</x:ref> = &lt;authority, defined in [RFC3986], Section 3.2&gt;
5117<x:ref>chunk</x:ref> = chunk-size *WSP [ chunk-ext ] CRLF chunk-data CRLF
5118<x:ref>chunk-data</x:ref> = 1*OCTET
5119<x:ref>chunk-ext</x:ref> = *( ";" *WSP chunk-ext-name [ "=" chunk-ext-val ] *WSP )
5120<x:ref>chunk-ext-name</x:ref> = token
5121<x:ref>chunk-ext-val</x:ref> = token / quoted-str-nf
5122<x:ref>chunk-size</x:ref> = 1*HEXDIG
5123<x:ref>comment</x:ref> = "(" *( ctext / quoted-cpair / comment ) ")"
5124<x:ref>connection-token</x:ref> = token
5125<x:ref>ctext</x:ref> = OWS / %x21-27 ; '!'-'''
5126 / %x2A-5B ; '*'-'['
5127 / %x5D-7E ; ']'-'~'
5128 / obs-text
5130<x:ref>date1</x:ref> = day SP month SP year
5131<x:ref>date2</x:ref> = day "-" month "-" 2DIGIT
5132<x:ref>date3</x:ref> = month SP ( 2DIGIT / ( SP DIGIT ) )
5133<x:ref>day</x:ref> = 2DIGIT
5134<x:ref>day-name</x:ref> = %x4D.6F.6E ; Mon
5135 / %x54.75.65 ; Tue
5136 / %x57.65.64 ; Wed
5137 / %x54.68.75 ; Thu
5138 / %x46.72.69 ; Fri
5139 / %x53.61.74 ; Sat
5140 / %x53.75.6E ; Sun
5141<x:ref>day-name-l</x:ref> = %x4D.6F.6E.64.61.79 ; Monday
5142 / %x54. ; Tuesday
5143 / %x57.65.64.6E. ; Wednesday
5144 / %x54. ; Thursday
5145 / %x46. ; Friday
5146 / %x53. ; Saturday
5147 / %x53.75.6E.64.61.79 ; Sunday
5149<x:ref>field-content</x:ref> = *( WSP / VCHAR / obs-text )
5150<x:ref>field-name</x:ref> = token
5151<x:ref>field-value</x:ref> = *( field-content / OWS )
5153<x:ref>header-field</x:ref> = field-name ":" OWS [ field-value ] OWS
5154<x:ref>hour</x:ref> = 2DIGIT
5155<x:ref>http-URI</x:ref> = "http://" authority path-abempty [ "?" query ]
5156<x:ref>https-URI</x:ref> = "https://" authority path-abempty [ "?" query ]
5158<x:ref>last-chunk</x:ref> = 1*"0" *WSP [ chunk-ext ] CRLF
5160<x:ref>message-body</x:ref> = *OCTET
5161<x:ref>minute</x:ref> = 2DIGIT
5162<x:ref>month</x:ref> = %x4A.61.6E ; Jan
5163 / %x46.65.62 ; Feb
5164 / %x4D.61.72 ; Mar
5165 / %x41.70.72 ; Apr
5166 / %x4D.61.79 ; May
5167 / %x4A.75.6E ; Jun
5168 / %x4A.75.6C ; Jul
5169 / %x41.75.67 ; Aug
5170 / %x53.65.70 ; Sep
5171 / %x4F.63.74 ; Oct
5172 / %x4E.6F.76 ; Nov
5173 / %x44.65.63 ; Dec
5175<x:ref>obs-date</x:ref> = rfc850-date / asctime-date
5176<x:ref>obs-fold</x:ref> = CRLF
5177<x:ref>obs-text</x:ref> = %x80-FF
5179<x:ref>partial-URI</x:ref> = relative-part [ "?" query ]
5180<x:ref>path-abempty</x:ref> = &lt;path-abempty, defined in [RFC3986], Section 3.3&gt;
5181<x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in [RFC3986], Section 3.3&gt;
5182<x:ref>port</x:ref> = &lt;port, defined in [RFC3986], Section 3.2.3&gt;
5183<x:ref>product</x:ref> = token [ "/" product-version ]
5184<x:ref>product-version</x:ref> = token
5185<x:ref>protocol-name</x:ref> = token
5186<x:ref>protocol-version</x:ref> = token
5187<x:ref>pseudonym</x:ref> = token
5189<x:ref>qdtext</x:ref> = OWS / "!" / %x23-5B ; '#'-'['
5190 / %x5D-7E ; ']'-'~'
5191 / obs-text
5192<x:ref>qdtext-nf</x:ref> = WSP / "!" / %x23-5B ; '#'-'['
5193 / %x5D-7E ; ']'-'~'
5194 / obs-text
5195<x:ref>query</x:ref> = &lt;query, defined in [RFC3986], Section 3.4&gt;
5196<x:ref>quoted-cpair</x:ref> = "\" ( WSP / VCHAR / obs-text )
5197<x:ref>quoted-pair</x:ref> = "\" ( WSP / VCHAR / obs-text )
5198<x:ref>quoted-str-nf</x:ref> = DQUOTE *( qdtext-nf / quoted-pair ) DQUOTE
5199<x:ref>quoted-string</x:ref> = DQUOTE *( qdtext / quoted-pair ) DQUOTE
5200<x:ref>qvalue</x:ref> = ( "0" [ "." *3DIGIT ] ) / ( "1" [ "." *3"0" ] )
5202<x:ref>received-by</x:ref> = ( uri-host [ ":" port ] ) / pseudonym
5203<x:ref>received-protocol</x:ref> = [ protocol-name "/" ] protocol-version
5204<x:ref>relative-part</x:ref> = &lt;relative-part, defined in [RFC3986], Section 4.2&gt;
5205<x:ref>request-header</x:ref> = &lt;request-header, defined in [Part2], Section 3&gt;
5206<x:ref>request-target</x:ref> = "*" / absolute-URI / ( path-absolute [ "?" query ] )
5207 / authority
5208<x:ref>response-header</x:ref> = &lt;response-header, defined in [Part2], Section 5&gt;
5209<x:ref>rfc1123-date</x:ref> = day-name "," SP date1 SP time-of-day SP GMT
5210<x:ref>rfc850-date</x:ref> = day-name-l "," SP date2 SP time-of-day SP GMT
5212<x:ref>second</x:ref> = 2DIGIT
5213<x:ref>special</x:ref> = "(" / ")" / "&lt;" / "&gt;" / "@" / "," / ";" / ":" / "\" /
5214 DQUOTE / "/" / "[" / "]" / "?" / "=" / "{" / "}"
5215<x:ref>start-line</x:ref> = Request-Line / Status-Line
5217<x:ref>t-codings</x:ref> = "trailers" / ( transfer-extension [ te-params ] )
5218<x:ref>tchar</x:ref> = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*" / "+" / "-" / "." /
5219 "^" / "_" / "`" / "|" / "~" / DIGIT / ALPHA
5220<x:ref>te-ext</x:ref> = OWS ";" OWS token [ "=" word ]
5221<x:ref>te-params</x:ref> = OWS ";" OWS "q=" qvalue *te-ext
5222<x:ref>time-of-day</x:ref> = hour ":" minute ":" second
5223<x:ref>token</x:ref> = 1*tchar
5224<x:ref>trailer-part</x:ref> = *( header-field CRLF )
5225<x:ref>transfer-coding</x:ref> = "chunked" / "compress" / "deflate" / "gzip" /
5226 transfer-extension
5227<x:ref>transfer-extension</x:ref> = token *( OWS ";" OWS transfer-parameter )
5228<x:ref>transfer-parameter</x:ref> = attribute BWS "=" BWS value
5230<x:ref>uri-host</x:ref> = &lt;host, defined in [RFC3986], Section 3.2.2&gt;
5232<x:ref>value</x:ref> = word
5234<x:ref>word</x:ref> = token / quoted-string
5236<x:ref>year</x:ref> = 4DIGIT
5239<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline">
5240; Cache-Control defined but not used
5241; Chunked-Body defined but not used
5242; Connection defined but not used
5243; Content-Length defined but not used
5244; Date defined but not used
5245; HTTP-message defined but not used
5246; Host defined but not used
5247; MIME-Version defined but not used
5248; Pragma defined but not used
5249; Request defined but not used
5250; Response defined but not used
5251; TE defined but not used
5252; Trailer defined but not used
5253; Transfer-Encoding defined but not used
5254; URI-reference defined but not used
5255; Upgrade defined but not used
5256; Via defined but not used
5257; Warning defined but not used
5258; http-URI defined but not used
5259; https-URI defined but not used
5260; partial-URI defined but not used
5261; request-header defined but not used
5262; response-header defined but not used
5263; special defined but not used
5265<?ENDINC p1-messaging.abnf-appendix ?>
5267<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
5269<section title="Since RFC 2616">
5271  Extracted relevant partitions from <xref target="RFC2616"/>.
5275<section title="Since draft-ietf-httpbis-p1-messaging-00">
5277  Closed issues:
5278  <list style="symbols">
5279    <t>
5280      <eref target=""/>:
5281      "HTTP Version should be case sensitive"
5282      (<eref target=""/>)
5283    </t>
5284    <t>
5285      <eref target=""/>:
5286      "'unsafe' characters"
5287      (<eref target=""/>)
5288    </t>
5289    <t>
5290      <eref target=""/>:
5291      "Chunk Size Definition"
5292      (<eref target=""/>)
5293    </t>
5294    <t>
5295      <eref target=""/>:
5296      "Message Length"
5297      (<eref target=""/>)
5298    </t>
5299    <t>
5300      <eref target=""/>:
5301      "Media Type Registrations"
5302      (<eref target=""/>)
5303    </t>
5304    <t>
5305      <eref target=""/>:
5306      "URI includes query"
5307      (<eref target=""/>)
5308    </t>
5309    <t>
5310      <eref target=""/>:
5311      "No close on 1xx responses"
5312      (<eref target=""/>)
5313    </t>
5314    <t>
5315      <eref target=""/>:
5316      "Remove 'identity' token references"
5317      (<eref target=""/>)
5318    </t>
5319    <t>
5320      <eref target=""/>:
5321      "Import query BNF"
5322    </t>
5323    <t>
5324      <eref target=""/>:
5325      "qdtext BNF"
5326    </t>
5327    <t>
5328      <eref target=""/>:
5329      "Normative and Informative references"
5330    </t>
5331    <t>
5332      <eref target=""/>:
5333      "RFC2606 Compliance"
5334    </t>
5335    <t>
5336      <eref target=""/>:
5337      "RFC977 reference"
5338    </t>
5339    <t>
5340      <eref target=""/>:
5341      "RFC1700 references"
5342    </t>
5343    <t>
5344      <eref target=""/>:
5345      "inconsistency in date format explanation"
5346    </t>
5347    <t>
5348      <eref target=""/>:
5349      "Date reference typo"
5350    </t>
5351    <t>
5352      <eref target=""/>:
5353      "Informative references"
5354    </t>
5355    <t>
5356      <eref target=""/>:
5357      "ISO-8859-1 Reference"
5358    </t>
5359    <t>
5360      <eref target=""/>:
5361      "Normative up-to-date references"
5362    </t>
5363  </list>
5366  Other changes:
5367  <list style="symbols">
5368    <t>
5369      Update media type registrations to use RFC4288 template.
5370    </t>
5371    <t>
5372      Use names of RFC4234 core rules DQUOTE and WSP,
5373      fix broken ABNF for chunk-data
5374      (work in progress on <eref target=""/>)
5375    </t>
5376  </list>
5380<section title="Since draft-ietf-httpbis-p1-messaging-01">
5382  Closed issues:
5383  <list style="symbols">
5384    <t>
5385      <eref target=""/>:
5386      "Bodies on GET (and other) requests"
5387    </t>
5388    <t>
5389      <eref target=""/>:
5390      "Updating to RFC4288"
5391    </t>
5392    <t>
5393      <eref target=""/>:
5394      "Status Code and Reason Phrase"
5395    </t>
5396    <t>
5397      <eref target=""/>:
5398      "rel_path not used"
5399    </t>
5400  </list>
5403  Ongoing work on ABNF conversion (<eref target=""/>):
5404  <list style="symbols">
5405    <t>
5406      Get rid of duplicate BNF rule names ("host" -> "uri-host", "trailer" ->
5407      "trailer-part").
5408    </t>
5409    <t>
5410      Avoid underscore character in rule names ("http_URL" ->
5411      "http-URL", "abs_path" -> "path-absolute").
5412    </t>
5413    <t>
5414      Add rules for terms imported from URI spec ("absoluteURI", "authority",
5415      "path-absolute", "port", "query", "relativeURI", "host) &mdash; these will
5416      have to be updated when switching over to RFC3986.
5417    </t>
5418    <t>
5419      Synchronize core rules with RFC5234.
5420    </t>
5421    <t>
5422      Get rid of prose rules that span multiple lines.
5423    </t>
5424    <t>
5425      Get rid of unused rules LOALPHA and UPALPHA.
5426    </t>
5427    <t>
5428      Move "Product Tokens" section (back) into Part 1, as "token" is used
5429      in the definition of the Upgrade header field.
5430    </t>
5431    <t>
5432      Add explicit references to BNF syntax and rules imported from other parts of the specification.
5433    </t>
5434    <t>
5435      Rewrite prose rule "token" in terms of "tchar", rewrite prose rule "TEXT".
5436    </t>
5437  </list>
5441<section title="Since draft-ietf-httpbis-p1-messaging-02" anchor="changes.since.02">
5443  Closed issues:
5444  <list style="symbols">
5445    <t>
5446      <eref target=""/>:
5447      "HTTP-date vs. rfc1123-date"
5448    </t>
5449    <t>
5450      <eref target=""/>:
5451      "WS in quoted-pair"
5452    </t>
5453  </list>
5456  Ongoing work on IANA Message Header Field Registration (<eref target=""/>):
5457  <list style="symbols">
5458    <t>
5459      Reference RFC 3984, and update header field registrations for headers defined
5460      in this document.
5461    </t>
5462  </list>
5465  Ongoing work on ABNF conversion (<eref target=""/>):
5466  <list style="symbols">
5467    <t>
5468      Replace string literals when the string really is case-sensitive (HTTP-Version).
5469    </t>
5470  </list>
5474<section title="Since draft-ietf-httpbis-p1-messaging-03" anchor="changes.since.03">
5476  Closed issues:
5477  <list style="symbols">
5478    <t>
5479      <eref target=""/>:
5480      "Connection closing"
5481    </t>
5482    <t>
5483      <eref target=""/>:
5484      "Move registrations and registry information to IANA Considerations"
5485    </t>
5486    <t>
5487      <eref target=""/>:
5488      "need new URL for PAD1995 reference"
5489    </t>
5490    <t>
5491      <eref target=""/>:
5492      "IANA Considerations: update HTTP URI scheme registration"
5493    </t>
5494    <t>
5495      <eref target=""/>:
5496      "Cite HTTPS URI scheme definition"
5497    </t>
5498    <t>
5499      <eref target=""/>:
5500      "List-type headers vs Set-Cookie"
5501    </t>
5502  </list>
5505  Ongoing work on ABNF conversion (<eref target=""/>):
5506  <list style="symbols">
5507    <t>
5508      Replace string literals when the string really is case-sensitive (HTTP-Date).
5509    </t>
5510    <t>
5511      Replace HEX by HEXDIG for future consistence with RFC 5234's core rules.
5512    </t>
5513  </list>
5517<section title="Since draft-ietf-httpbis-p1-messaging-04" anchor="changes.since.04">
5519  Closed issues:
5520  <list style="symbols">
5521    <t>
5522      <eref target=""/>:
5523      "Out-of-date reference for URIs"
5524    </t>
5525    <t>
5526      <eref target=""/>:
5527      "RFC 2822 is updated by RFC 5322"
5528    </t>
5529  </list>
5532  Ongoing work on ABNF conversion (<eref target=""/>):
5533  <list style="symbols">
5534    <t>
5535      Use "/" instead of "|" for alternatives.
5536    </t>
5537    <t>
5538      Get rid of RFC822 dependency; use RFC5234 plus extensions instead.
5539    </t>
5540    <t>
5541      Only reference RFC 5234's core rules.
5542    </t>
5543    <t>
5544      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
5545      whitespace ("OWS") and required whitespace ("RWS").
5546    </t>
5547    <t>
5548      Rewrite ABNFs to spell out whitespace rules, factor out
5549      header field value format definitions.
5550    </t>
5551  </list>
5555<section title="Since draft-ietf-httpbis-p1-messaging-05" anchor="changes.since.05">
5557  Closed issues:
5558  <list style="symbols">
5559    <t>
5560      <eref target=""/>:
5561      "Header LWS"
5562    </t>
5563    <t>
5564      <eref target=""/>:
5565      "Sort 1.3 Terminology"
5566    </t>
5567    <t>
5568      <eref target=""/>:
5569      "RFC2047 encoded words"
5570    </t>
5571    <t>
5572      <eref target=""/>:
5573      "Character Encodings in TEXT"
5574    </t>
5575    <t>
5576      <eref target=""/>:
5577      "Line Folding"
5578    </t>
5579    <t>
5580      <eref target=""/>:
5581      "OPTIONS * and proxies"
5582    </t>
5583    <t>
5584      <eref target=""/>:
5585      "Reason-Phrase BNF"
5586    </t>
5587    <t>
5588      <eref target=""/>:
5589      "Use of TEXT"
5590    </t>
5591    <t>
5592      <eref target=""/>:
5593      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
5594    </t>
5595    <t>
5596      <eref target=""/>:
5597      "RFC822 reference left in discussion of date formats"
5598    </t>
5599  </list>
5602  Final work on ABNF conversion (<eref target=""/>):
5603  <list style="symbols">
5604    <t>
5605      Rewrite definition of list rules, deprecate empty list elements.
5606    </t>
5607    <t>
5608      Add appendix containing collected and expanded ABNF.
5609    </t>
5610  </list>
5613  Other changes:
5614  <list style="symbols">
5615    <t>
5616      Rewrite introduction; add mostly new Architecture Section.
5617    </t>
5618    <t>
5619      Move definition of quality values from Part 3 into Part 1;
5620      make TE request header field grammar independent of accept-params (defined in Part 3).
5621    </t>
5622  </list>
5626<section title="Since draft-ietf-httpbis-p1-messaging-06" anchor="changes.since.06">
5628  Closed issues:
5629  <list style="symbols">
5630    <t>
5631      <eref target=""/>:
5632      "base for numeric protocol elements"
5633    </t>
5634    <t>
5635      <eref target=""/>:
5636      "comment ABNF"
5637    </t>
5638  </list>
5641  Partly resolved issues:
5642  <list style="symbols">
5643    <t>
5644      <eref target=""/>:
5645      "205 Bodies" (took out language that implied that there might be
5646      methods for which a request body MUST NOT be included)
5647    </t>
5648    <t>
5649      <eref target=""/>:
5650      "editorial improvements around HTTP-date"
5651    </t>
5652  </list>
5656<section title="Since draft-ietf-httpbis-p1-messaging-07" anchor="changes.since.07">
5658  Closed issues:
5659  <list style="symbols">
5660    <t>
5661      <eref target=""/>:
5662      "Repeating single-value headers"
5663    </t>
5664    <t>
5665      <eref target=""/>:
5666      "increase connection limit"
5667    </t>
5668    <t>
5669      <eref target=""/>:
5670      "IP addresses in URLs"
5671    </t>
5672    <t>
5673      <eref target=""/>:
5674      "take over HTTP Upgrade Token Registry"
5675    </t>
5676    <t>
5677      <eref target=""/>:
5678      "CR and LF in chunk extension values"
5679    </t>
5680    <t>
5681      <eref target=""/>:
5682      "HTTP/0.9 support"
5683    </t>
5684    <t>
5685      <eref target=""/>:
5686      "pick IANA policy (RFC5226) for Transfer Coding / Content Coding"
5687    </t>
5688    <t>
5689      <eref target=""/>:
5690      "move definitions of gzip/deflate/compress to part 1"
5691    </t>
5692    <t>
5693      <eref target=""/>:
5694      "disallow control characters in quoted-pair"
5695    </t>
5696  </list>
5699  Partly resolved issues:
5700  <list style="symbols">
5701    <t>
5702      <eref target=""/>:
5703      "update IANA requirements wrt Transfer-Coding values" (add the
5704      IANA Considerations subsection)
5705    </t>
5706  </list>
5710<section title="Since draft-ietf-httpbis-p1-messaging-08" anchor="changes.since.08">
5712  Closed issues:
5713  <list style="symbols">
5714    <t>
5715      <eref target=""/>:
5716      "header parsing, treatment of leading and trailing OWS"
5717    </t>
5718  </list>
5721  Partly resolved issues:
5722  <list style="symbols">
5723    <t>
5724      <eref target=""/>:
5725      "Placement of 13.5.1 and 13.5.2"
5726    </t>
5727    <t>
5728      <eref target=""/>:
5729      "use of term "word" when talking about header structure"
5730    </t>
5731  </list>
5735<section title="Since draft-ietf-httpbis-p1-messaging-09" anchor="changes.since.09">
5737  Closed issues:
5738  <list style="symbols">
5739    <t>
5740      <eref target=""/>:
5741      "Clarification of the term 'deflate'"
5742    </t>
5743    <t>
5744      <eref target=""/>:
5745      "OPTIONS * and proxies"
5746    </t>
5747    <t>
5748      <eref target=""/>:
5749      "MIME-Version not listed in P1, general header fields"
5750    </t>
5751    <t>
5752      <eref target=""/>:
5753      "IANA registry for content/transfer encodings"
5754    </t>
5755    <t>
5756      <eref target=""/>:
5757      "Case-sensitivity of HTTP-date"
5758    </t>
5759    <t>
5760      <eref target=""/>:
5761      "use of term "word" when talking about header structure"
5762    </t>
5763  </list>
5766  Partly resolved issues:
5767  <list style="symbols">
5768    <t>
5769      <eref target=""/>:
5770      "Term for the requested resource's URI"
5771    </t>
5772  </list>
5776<section title="Since draft-ietf-httpbis-p1-messaging-10" anchor="changes.since.10">
5778  Closed issues:
5779  <list style="symbols">
5780    <t>
5781      <eref target=""/>:
5782      "Connection Closing"
5783    </t>
5784    <t>
5785      <eref target=""/>:
5786      "Delimiting messages with multipart/byteranges"
5787    </t>
5788    <t>
5789      <eref target=""/>:
5790      "Handling multiple Content-Length headers"
5791    </t>
5792    <t>
5793      <eref target=""/>:
5794      "Clarify entity / representation / variant terminology"
5795    </t>
5796    <t>
5797      <eref target=""/>:
5798      "consider removing the 'changes from 2068' sections"
5799    </t>
5800  </list>
5803  Partly resolved issues:
5804  <list style="symbols">
5805    <t>
5806      <eref target=""/>:
5807      "HTTP(s) URI scheme definitions"
5808    </t>
5809  </list>
5813<section title="Since draft-ietf-httpbis-p1-messaging-11" anchor="changes.since.11">
5815  Closed issues:
5816  <list style="symbols">
5817    <t>
5818      <eref target=""/>:
5819      "Trailer requirements"
5820    </t>
5821    <t>
5822      <eref target=""/>:
5823      "Text about clock requirement for caches belongs in p6"
5824    </t>
5825    <t>
5826      <eref target=""/>:
5827      "effective request URI: handling of missing host in HTTP/1.0"
5828    </t>
5829    <t>
5830      <eref target=""/>:
5831      "confusing Date requirements for clients"
5832    </t>
5833  </list>
5836  Partly resolved issues:
5837  <list style="symbols">
5838    <t>
5839      <eref target=""/>:
5840      "Handling multiple Content-Length headers"
5841    </t>
5842  </list>
5846<section title="Since draft-ietf-httpbis-p1-messaging-12" anchor="changes.since.12">
5848  Closed issues:
5849  <list style="symbols">
5850    <t>
5851      <eref target=""/>:
5852      "RFC2145 Normative"
5853    </t>
5854    <t>
5855      <eref target=""/>:
5856      "HTTP(s) URI scheme definitions" (tune the requirements on userinfo)
5857    </t>
5858    <t>
5859      <eref target=""/>:
5860      "define 'transparent' proxy"
5861    </t>
5862    <t>
5863      <eref target=""/>:
5864      "Is * usable as a request-uri for new methods?"
5865    </t>
5866    <t>
5867      <eref target=""/>:
5868      "Migrate Upgrade details from RFC2817"
5869    </t>
5870    <t>
5871      <eref target=""/>:
5872      "untangle ABNFs for header fields"
5873    </t>
5874    <t>
5875      <eref target=""/>:
5876      "update RFC 2109 reference"
5877    </t>
5878  </list>
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